$$\text{For example,}$$ $$x^3 - 1, 4a^3 - 100a^2 + a - 6$$ $$\text{and}$$ $$m^2n + mn^2$$ $$\text{are all cubic polynomials.}$$
$$\text{(a) In the polynomial}$$ $$p(x),$$ $$\text{the variable is}$$ $$x.$$
$$\text{So, the cubic polynomial should be in terms of}$$ $$x$$ $$\text{only.}$$
$$\text{But here,}$$ $$p(x)=y^3-27,$$ $$\text{in which the cubic polynomial is in terms of variable}$$ $$y$$.
$$\text{Therefore,}$$ $$p(x)=y^3-27$$ $$\text{is not a cubic polynomial.}$$
$$\text{(b) In the polynomial}$$ $$p(y),$$ $$\text{the variable is}$$ $$y$$. $$\text{So, the cubic polynomial should be in terms of}$$ $$y$$
$$\text{ only, But here,}$$ $$p(y)=x^3-27,$$ $$\text{in which the cubic polynomial is in terms of variable}$$ $$x$$.
$$\text{Therefore,}$$ $$p(y)=x^3-27$$ $$\text{is not a cubic polynomial.}$$
$$\text{(c) In the polynomial}$$ $$p(x),$$ $$\text{the variable is}$$ $$x$$. $$\text{So, the cubic polynomial should be in terms of}$$ $$x$$
$$\text{only, But here,}$$ $$p(x)=x^3-27,$$ $$\text{in which the cubic polynomial is in terms of variable}$$ $$x$$.
$$\text{So,}$$ $$p(x)=x^3-27$$ $$\text{is a cubic polynomial.}$$
. $$\text{(d) In the polynomial}$$ $$p(y),$$ $$\text{the variable is}$$ $$y$$. $$\text{So, the cubic polynomial should be in terms of}$$ $$y$$
$$\text{ only, But here,}$$ $$p(y)=27,$$ $$\text{in which there is only constant}$$ $$x$$.
$$\text{Therefore,}$$ $$p(y)=27$$ $$\text{is not a cubic polynomial.}$$
$$\textbf{Hence, correct option is C}$$