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[passage-header](This passage is adapted from Alan Ehrenhalt, The Great Inversion and the Future of the American City, 2013, Vintage. Demographic inversion is a phenomenon that describes the rearrangement of living patterns throughout a metropolitan area.)[/passage-header]   84546We are not witnessing the abandonment of the suburbs, or a movement of millions of people back to the city all at once. The 2010 census certainly did not turn up evidence of a middle-class stampede to the nations cities. The news was mixed: Some of the larger cities on the East Coast tended to gain population, albeit in small increments. Those in the Midwest, including Chicago, tended to lose substantial numbers. The cities that showed gains in overall population during the entire decade tended to be in the South and Southwest. But when it comes to measuring demographic inversion, raw census numbers are an ineffective blunt instrument. A closer look at the results shows that the most powerful demographic events of the past decade were the movement of African Americans out of central cities (180,000 of them in Chicago alone) and the settlement of immigrant groups in suburbs, often ones many miles distant from downtown. Central-city areas that gained affluent residents in the first part of the decade maintained that population in the recession years from 2007 to 2009. They also, according to a 2011 study by Brookings, suffered considerably less from increased unemployment than the suburbs did. Not many young professionals moved to new downtown condos in the recession years because few such residences were being built. But there is no reason to believe that the demographic trends prevailing prior to the construction, the bust will not resume once that bust is over. It is important to remember that demographic inversion is not a proxy for population growth; it can occur in cities that are growing, those whose numbers are 42279flat, and even in those undergoing a modest decline in size55758.
   18230America's major cities face enormous fiscal problems, many of them the result of public pension obligations they incurred in the most prosperous years of the past two decades79283. Some, Chicago prominent among them, simply are not producing enough revenue to support the level of public services to which most of the citizens have grown to feel entitled. 61787How the cities are going to solve this problem, I do not know88247. 37289What I do know is that if the fiscal crisis was going to drive affluent professionals out of central cities, it would have done so by now30124. There is no evidence that it has.
   83920The truth is that we are living at a moment in which the massive outward migration of the affluent that characterized the second half of the twentieth century is coming to an end88980. And we need to adjust our perceptions of cities, suburbs, and urban mobility as a result.
   95791Much of our perspective on the process of metropolitan settlement dates, whether we realize it or not, from a paper written in 1925 by the University of Chicago sociologist Ernest W. Burgess33441. 13243It was Burgess who defined four urban/suburban zones of settlement38894: a central business district; an area of manufacturing just beyond it; then a residential area inhabited by the industrial and immigrant working class; and finally an outer enclave of single-family dwellings.
   Burgess was right about the urban America of 1925; he was right about the urban America of 1974. 64755Virtually every city in the country had a downtown, where the commercial life of the metropolis was 80798conducted; it had a factory district just beyond; it had districts of working-class residences just beyond that, and it had residential suburbs for the wealthy and the upper middle class at the far end of the continuum69291. 28352As a family moved up the economic ladder, it also moved outward from crowded working-class districts to more spacious apartments and, eventually, to a suburban home94921. The suburbs of Burgess's time bore little resemblance to those at the end of the twentieth century, but the theory still essentially worked. People moved ahead in life by moving farther out.
   But in the past decade, in quite a few places, this model has ceased to describe reality. There are still downtown commercial districts, but there are no factory districts lying next to them. There are scarcely any factories at all. These close-in parts of the city, whose few residents Burgess described as dwelling in "submerged regions of poverty, degradation, and disease", are increasingly the preserve of the affluent who work in the commercial core. And just as crucially newcomers to America are not settling on the inside and accumulating the resources to move out; they are living in the suburbs from day one.

[passage-header](This passage is adapted from Alan Ehrenhalt, The Great Inversion and the Future of the American City, 2013, Vintage. Demographic inversion is a phenomenon that describes the rearrangement of living patterns throughout a metropolitan area.)[/passage-header]   84546We are not witnessing the abandonment of the suburbs, or a movement of millions of people back to the city all at once. The 2010 census certainly did not turn up evidence of a middle-class stampede to the nations cities. The news was mixed: Some of the larger cities on the East Coast tended to gain population, albeit in small increments. Those in the Midwest, including Chicago, tended to lose substantial numbers. The cities that showed gains in overall population during the entire decade tended to be in the South and Southwest. But when it comes to measuring demographic inversion, raw census numbers are an ineffective blunt instrument. A closer look at the results shows that the most powerful demographic events of the past decade were the movement of African Americans out of central cities (180,000 of them in Chicago alone) and the settlement of immigrant groups in suburbs, often ones many miles distant from downtown. Central-city areas that gained affluent residents in the first part of the decade maintained that population in the recession years from 2007 to 2009. They also, according to a 2011 study by Brookings, suffered considerably less from increased unemployment than the suburbs did. Not many young professionals moved to new downtown condos in the recession years because few such residences were being built. But there is no reason to believe that the demographic trends prevailing prior to the construction, the bust will not resume once that bust is over. It is important to remember that demographic inversion is not a proxy for population growth; it can occur in cities that are growing, those whose numbers are 42279flat, and even in those undergoing a modest decline in size55758.
   18230America's major cities face enormous fiscal problems, many of them the result of public pension obligations they incurred in the most prosperous years of the past two decades79283. Some, Chicago prominent among them, simply are not producing enough revenue to support the level of public services to which most of the citizens have grown to feel entitled. 61787How the cities are going to solve this problem, I do not know88247. 37289What I do know is that if the fiscal crisis was going to drive affluent professionals out of central cities, it would have done so by now30124. There is no evidence that it has.
   83920The truth is that we are living at a moment in which the massive outward migration of the affluent that characterized the second half of the twentieth century is coming to an end88980. And we need to adjust our perceptions of cities, suburbs, and urban mobility as a result.
   95791Much of our perspective on the process of metropolitan settlement dates, whether we realize it or not, from a paper written in 1925 by the University of Chicago sociologist Ernest W. Burgess33441. 13243It was Burgess who defined four urban/suburban zones of settlement38894: a central business district; an area of manufacturing just beyond it; then a residential area inhabited by the industrial and immigrant working class; and finally an outer enclave of single-family dwellings.
   Burgess was right about the urban America of 1925; he was right about the urban America of 1974. 64755Virtually every city in the country had a downtown, where the commercial life of the metropolis was 80798conducted; it had a factory district just beyond; it had districts of working-class residences just beyond that, and it had residential suburbs for the wealthy and the upper middle class at the far end of the continuum69291. 28352As a family moved up the economic ladder, it also moved outward from crowded working-class districts to more spacious apartments and, eventually, to a suburban home94921. The suburbs of Burgess's time bore little resemblance to those at the end of the twentieth century, but the theory still essentially worked. People moved ahead in life by moving farther out.
   But in the past decade, in quite a few places, this model has ceased to describe reality. There are still downtown commercial districts, but there are no factory districts lying next to them. There are scarcely any factories at all. These close-in parts of the city, whose few residents Burgess described as dwelling in "submerged regions of poverty, degradation, and disease", are increasingly the preserve of the affluent who work in the commercial core. And just as crucially newcomers to America are not settling on the inside and accumulating the resources to move out; they are living in the suburbs from day one.

[passage-header]How Do You Like Those Apples?[/passage-header]Marketed as SmartFresh, the chemical 1-MCP (1-methylcyclopropene) has been used by fruit growers since 2002 in the United States and elsewhere to preserve the crispness and lengthen the storage life of apples and other fruit, which often must travel long distances before being eaten by consumers. (23) 1-MCP lengthens storage life by three to four times when applied to apples. This extended life allows producers to sell their apples in the off-season, months after the apples have been harvested. And at a cost of about one cent per pound of apples,
1-MCP is a highly cost-effective treatment. However, 1-MCP is not a panacea for fruit producers or sellers: there are problems and limitations associated with its use. [1] 1-MCP works by limiting a fruits production of ethylene, (24) it is a chemical that causes fruit to ripen and eventually rot. [2]While 1-MCP keeps apples (25) tight and crisp for months, it also limits (26) their scent production. [3] This may not be much of a problem with certain kinds of apples that are not naturally very fragrant, such as Granny Smith, but for apples that are prized for their fruity fragrance, such as McIntosh, this can be a problem with consumers, (27) that will reject apples lacking the expected aroma. [4] But some fruits do not respond as well to 1-MCP as others (28) did, and some even respond adversely. [5] Furthermore, some fruits, particularly those that naturally produce a large amount of ethylene, do not respond as well to 1-MCP treatment. [6] Take Bartlett (29) pears; for instance, unless they are treated with exactly the right amount of 1-MCP at exactly the right time, they will remain hard and green until they rot, and consumers who experience this will be unlikely to purchase them again.[passage-footer]Adapted from Hannah J. James, Jacqueline F. Nock, and Chris B. Watkins, The Failure of Postharvest Treatments to Control Firm Flesh Browning in Empire Apples. 2010 by The New York State Horticultural Society.[/passage-footer]

[passage-header]Read the passage and answer the question that follows:
(This passage is adapted from Emily Anthes, Frankenstein's Cat, 2013.)[/passage-header]   When scientists first learned how to edit the genomes of animals, they began to imagine all the ways they could use this new power. Creating brightly colored novelty pets was not a high priority. Instead, most researchers envisioned far more consequential applications, hoping to create genetically engineered animals that saved human lives. One enterprise is now delivering on this dream. Welcome to the world of pharming, in which simple genetic tweaks turn animals into living pharmaceutical factories.
   53499Many of the proteins that our cells crank out naturally make for good medicine. Our bodies' own enzymes, hormones, clotting factors, and antibodies are commonly used to treat cancer, diabetes, autoimmune diseases, and more93455. 42998The trouble is that its difficult and expensive to make these compounds on an industrial scale, and as a result, patients can face shortages of the medicines they need. Dairy animals, on the other hand, are 41493expert protein producers, their udders swollen with milk45597. So the creation of the first transgenic animals---first mice, then other species---in the 1980s gave scientists an idea: What 65143if they put the gene for a human antibody or enzyme into a cow, goat, or sheep? If they put the gene in just the right place, under the control of the right molecular switch, maybe they could engineer animals that produced healing human proteins in their milk59518. Then doctors could collect medicine by the bucketful.
    Throughout the 1980s and '90s, studies provided proof of principle, as scientists created transgenic mice, sheep, goats, pigs, cattle, and rabbits that did, in fact, make therapeutic compounds in their milk.
   94444At first, this work was merely gee-whiz, scientific geekery, lab-bound thought experiments come true34533. 80905That all changed with ATryn, a drug produced by the Massachusetts firm GTC Biotherapeutics. ATryn is antithrombin, an anticoagulant that can be used to prevent life-threatening blood clots10651. The compound, made by our liver cells, plays a key role in keeping our bodies clot-free. 86900It acts as a molecular bouncer, sidling up to clot-forming compounds and escorting them out of the bloodstream46291. 71054But as many as 1 in 2,000 Americans are born with a genetic mutation that prevents them from making antithrombin74998. These patients are prone to clots, especially in their legs and lungs, and they are at elevated risk of suffering from fatal complications during surgery and childbirth. Supplemental antithrombin can reduce this risk, and GTC decided to try to manufacture the compound using genetically engineered goats.
    To create its special herd of goats, GTC used microinjection, the same technique that produced GloFish and AquAdvantage salmon. The company's scientists took the gene for human antithrombin and injected it directly into fertilized goat eggs. Then they implanted the eggs in the wombs of 68619female goats. When the kids were born, some of them proved to be transgenic, the human gene nestled safely in their cells. 53784The researchers paired the antithrombin gene with a promoter (94525which is a sequence of DNA that controls gene activity81896) that is normally active in the goat's mammary glands during milk production91149. 

[passage-header]Read the passage and answer the question that follows:
(This passage is adapted from Emily Anthes, Frankenstein's Cat, 2013.)[/passage-header]   When scientists first learned how to edit the genomes of animals, they began to imagine all the ways they could use this new power. Creating brightly colored novelty pets was not a high priority. Instead, most researchers envisioned far more consequential applications, hoping to create genetically engineered animals that saved human lives. One enterprise is now delivering on this dream. Welcome to the world of pharming, in which simple genetic tweaks turn animals into living pharmaceutical factories.
   53499Many of the proteins that our cells crank out naturally make for good medicine. Our bodies' own enzymes, hormones, clotting factors, and antibodies are commonly used to treat cancer, diabetes, autoimmune diseases, and more93455. 42998The trouble is that its difficult and expensive to make these compounds on an industrial scale, and as a result, patients can face shortages of the medicines they need. Dairy animals, on the other hand, are 41493expert protein producers, their udders swollen with milk45597. So the creation of the first transgenic animals---first mice, then other species---in the 1980s gave scientists an idea: What 65143if they put the gene for a human antibody or enzyme into a cow, goat, or sheep? If they put the gene in just the right place, under the control of the right molecular switch, maybe they could engineer animals that produced healing human proteins in their milk59518. Then doctors could collect medicine by the bucketful.
    Throughout the 1980s and '90s, studies provided proof of principle, as scientists created transgenic mice, sheep, goats, pigs, cattle, and rabbits that did, in fact, make therapeutic compounds in their milk.
   94444At first, this work was merely gee-whiz, scientific geekery, lab-bound thought experiments come true34533. 80905That all changed with ATryn, a drug produced by the Massachusetts firm GTC Biotherapeutics. ATryn is antithrombin, an anticoagulant that can be used to prevent life-threatening blood clots10651. The compound, made by our liver cells, plays a key role in keeping our bodies clot-free. 86900It acts as a molecular bouncer, sidling up to clot-forming compounds and escorting them out of the bloodstream46291. 71054But as many as 1 in 2,000 Americans are born with a genetic mutation that prevents them from making antithrombin74998. These patients are prone to clots, especially in their legs and lungs, and they are at elevated risk of suffering from fatal complications during surgery and childbirth. Supplemental antithrombin can reduce this risk, and GTC decided to try to manufacture the compound using genetically engineered goats.
    To create its special herd of goats, GTC used microinjection, the same technique that produced GloFish and AquAdvantage salmon. The company's scientists took the gene for human antithrombin and injected it directly into fertilized goat eggs. Then they implanted the eggs in the wombs of 68619female goats. When the kids were born, some of them proved to be transgenic, the human gene nestled safely in their cells. 53784The researchers paired the antithrombin gene with a promoter (94525which is a sequence of DNA that controls gene activity81896) that is normally active in the goat's mammary glands during milk production91149. 

[passage-header](This passage is adapted from Carolyn Gramling, Source of Mysterious Medieval Eruption Identified, 2013, American Association for the Advancement of Science.)[/passage-header]   77978About 750 years ago, a powerful volcano erupted somewhere on Earth, kicking off a centuries-long cold snap known as the Little Ice Age77954. 54549Identifying the volcano responsible has been tricky.
   That a powerful volcano erupted somewhere in the world, sometime in the Middle Ages, 27014is written in polar ice cores in the form of layers of sulfate deposits and tiny shards of volcanic glass. These cores suggest that the amount of sulfur the mystery volcano sent into the stratosphere put it firmly among the ranks of the strongest climate-perturbing eruptions of the current geological epoch, the Holocene, a period that stretches from 10,000 years ago to the present. A haze of stratospheric sulfur cools the climate by reflecting solar energy back into space.
   61911In 2012, a team of scientists led by geochemist Gifford Miller strengthened the link between the mystery eruption and the onset of the Little Ice Age by using radiocarbon dating of dead plant material from beneath the ice caps on Baffin Island and Iceland, as well as ice and sediment core data, to determine that the cold summers and ice growth began abruptly between 1275 and 1300 C.E. (and became intensified between 1430 and 1455 C.E.)56063. 96005Such a sudden onset pointed to a huge volcanic eruption injecting sulfur into the stratosphere and starting the cooling59626. Subsequently, unusually large and frequent eruptions of other volcanoes, as well as sea-ice/ocean feedbacks persisting long after the aerosols have been removed from the atmosphere, may have prolonged the cooling through the 1700s.
   Volcanologist Franck Lavigne and colleagues now think they've identified the volcano in question: Indonesia's Samalas. One line of evidence, they note, is historical records. According to Babad Lombok, records of the island written on palm leaves in Old Javanese, Samalas erupted catastrophically before the end of the 13th century, devastating surrounding villages---including Lombok's capital at the time, Pamatan---with ash and fast-moving sweeps of hot rock and gas called pyroclastic flows.
   72736The researchers then began to reconstruct the formation of the large, 800-meter-deep caldera [a basin-shaped volcanic crater] that now sits atop the volcano17025. 79677They examined 130 outcrops on the flanks of the volcano, exposing sequences of pumice---ash hardened into rock---and other pyroclastic material98225. 62558The volume of ash deposited, and the estimated height of the eruption plume (43 kilometers above sea level) put the eruption's magnitude at a minimum of 7 on the volcanic explosivity index (which has a scale of 1 to 8) -- making it one of the largest known in the Holocene57299.
   22551The team also performed radiocarbon analysis on carbonized tree trunks and branches buried within the pyroclastic deposits to confirm the date of the eruption; it could not, they concluded, have happened before 1257 C.E., and certainly happened in the 13th century23198.
   28275It's not a total surprise that an Indonesian volcano might be the source of the eruption, Miller says. "An equatorial eruption is more consistent with the apparent climate impacts65709." And, he adds, with sulfate appearing in both polar ice caps -- Arctic and Antarctic -- there is "a strong consensus" that this also supports an equatorial source.
   98371Another possible candidate -- both in terms of timing and geographical location -- is Ecuador's Quilotoa, estimated to have lasted erupted between 1147 and 1320 C.E. 62895But when Lavigne's team examined shards of volcanic glass from this volcano, they found that they didn't match the chemical composition of the glass found in polar ice cores, whereas the Samalas glass is a much closer match31324. That, they suggest, further strengthens the case that Samalas was responsible for the medieval "year without summer" in 1258 C.E.

[passage-header]Read the passage given below and answer the question that follows:[/passage-header]People around the world unanimously agree that gold is a valuable mineral. Gold has been seen as a precious commodity by many cultures throughout time, and Americans of the 1840s were no different. When James W. Marshall, a carpenter and sawmill owner, discovered a gold nugget in the American River, California was forever changed. News of his discovery attracted thousands of immigrants from other parts of California, as well as other places around the United States and the World.
   In the Sierra Nevada, a mountain range that runs 400 miles through California, years of erosion caused by rainfall and the downhill flow of mountain streams loosened pieces of gold that had been embedded in the solid rock formed over 100 million years ago. California is largely made of quartz previously found at the bottom of the Pacific Ocean. Underwater volcanoes melted the quartz into magma and pushed it up towards the surface, sometimes forming islands. Due to the movements of the Earth's tectonic plates, these islands were pushed together and against the West Coast. This movement and accumulation of land over millions of years formed the area known as California. The gold that was dispersed across the sea floor became concentrated and redistribution throughout the veins of quartz in the Sierra Nevada Mountains. 

[passage-header]Read the passage given below and answer the question that follows:[/passage-header]People around the world unanimously agree that gold is a valuable mineral. Gold has been seen as a precious commodity by many cultures throughout time, and Americans of the 1840s were no different. When James W. Marshall, a carpenter and sawmill owner, discovered a gold nugget in the American River, California was forever changed. News of his discovery attracted thousands of immigrants from other parts of California, as well as other places around the United States and the World.
   In the Sierra Nevada, a mountain range that runs 400 miles through California, years of erosion caused by rainfall and the downhill flow of mountain streams loosened pieces of gold that had been embedded in the solid rock formed over 100 million years ago. California is largely made of quartz previously found at the bottom of the Pacific Ocean. Underwater volcanoes melted the quartz into magma and pushed it up towards the surface, sometimes forming islands. Due to the movements of the Earth's tectonic plates, these islands were pushed together and against the West Coast. This movement and accumulation of land over millions of years formed the area known as California. The gold that was dispersed across the sea floor became concentrated and redistribution throughout the veins of quartz in the Sierra Nevada Mountains. 

[passage-header]This passage discusses the cane toad's introduction to and effect on the Australian environment.[/passage-header]   The cane toad, a large, brightly colored amphibian that can weigh more than around, was first introduced to the Australian continent by the sugarcane industry. The cane toad was a known predator of the cane beetle, which had been devouring the sugarcane crops since the early 1900s. Australian farmers thought that by importing these toads from their native habitats in the Americans, they could use the toads effectively to feast on pests like the cane beetle and eradicate the growing insect threat. So, in 1935, roughly 100 cane toads were carefully packed into crates and shipped to Australia. Upon their toad's arrival, the cane farmers eagerly brought them to a pond in the northeast province of Queensland. Before long, the female cane toads had laid hundreds of thousands of eggs in elongated, gelatinous strings, and the farmers waited for their new predators to be born. As the eggs hatched, the pond became filled with great clouds of squirming, wriggling tadpoles that, upon reaching maturity, were taken to the sugarcane fields and turned loose. The situation that resulted from this fateful release, however, did not coincide with the farmer's plan. Infact, the introduction of cane toads into the wild in Australia has since been deemed nothing short of an ecological disaster.
   Easily numbering well into the millions-an exact figure has been impossible to calculate the cane toads soon dominated the landscape in Queensland. Following their release, some of the toads descended as planned on the sugarcane crops and began to eat the beetles. However, they soon lost interest in their new habitat. For one thing, the mature cane beetles could fly away from their predators, forcing these slow, fat toads to work very hard for their food. In addition, the fields were hot and dry and provided little sleeping shelter for the newcomers, who generally prefer wet shade. These adverse conditions were not severe enough to kill off the toads, but instead, the toads began to look elsewhere for food and shelter. Nearby towns, full of lush gardens and well-watered lawns, were extremely inviting, and soon the toads had overrun entire residential areas. They covered the lawns, filled the gardens, found shelter under flowerpots or on porches, and even began to eat bowls of food left outside for pets like cats and dogs.
   Today, the people of Queensland hunt cane toads as if they were mosquitoes. But the toads continue to spread south and west through Australia in staggering numbers. As for the sugarcane industry, just five years after the release of the toads, an effective insecticide spray became available, and the cane beetles were easily exterminated. Scientists as well as the Australian government, however, continue to grapple with the cane toad problem.

[passage-header]The following passage discusses facts and speculation about a spy during the American Revolution.[/passage-header]

   Although he may not have been the first American spy, when Captain Nathan Hale uttered his famous final words, "I only regret I have but one life to lose for my country," he likely ensured that he would long be remembered as the first patriotic martyr of the American Revolution. Even today, Hale's story serves as an inspiration for others who have chosen to enter the often deadly and thankless profession of covert intelligence gathering. Yet, as it seems clear that the sacrifice Hale made in the autumn of 1776 will long be valued, relatively little is actually known about his fateful mission.