The word 'meander' means to take an indirect course in order to reach a destination. The river is taking any route it can find, any direction it can go through to join the sea. It isn't flowing through a straight path but goes in whichever direction it can find as it flows toward the sea, going zigzag. Option D provides the similar meaning as 'meandered', as the river is going in a zigzag way. 'Zigzag' means 'having frequent sharp turns', like the river. Hence option D is correct. The phrase 'swirled swiftly' means to 'twist or curl around' in a quick manner. Its meaning is slightly similar to 'meandered', but it isn't the correct option because 'swirled' refers to a spinning or whirling pattern that goes round and round, whereas the river is not following a whirling pattern. Hence option A is incorrect. 'Cascaded downhill' refers to a waterfall that is descending over a steep surface. As the word 'meandered' does not suggest a waterfall or even a steep surface, option B is incorrect. Similarly, option C is incorrect because it means 'water flowing from a height over a steep surface' and this is not the same meaning as 'meandered'.