Trong bốn giới hạn sau đây, giới hạn nào bằng 0?

Đáp án đúng là: C

$$\begin{gathered} \lim \frac{1-n^3}{n^2+2n}=\lim \frac{\frac{1}{n^3}-1}{\frac{1}{n}+\frac{2}{n^2}}=-\infty \\ \lim \frac{\left(2n+1\right){\left(n-3\right)}^2}{n-2n^3}=\lim \frac{\left(2+\frac{1}{n}\right){\left(1-\frac{3}{n}\right)}^2}{\frac{1}{n^2}-2}=\frac{2.1}{-2}=-1 \\ \lim \frac{2^n+1}{{3.2}^n-3^n}=\lim \frac{{\left(\frac{2}{3}\right)}^n+{\left(\frac{1}{3}\right)}^n}{3.{\left(\frac{2}{3}\right)}^n-1}=0 \\ \lim \frac{{\displaystyle 2^n+3}}{{\displaystyle 1-2^n}}=\lim \frac{{\displaystyle 1+\frac{{\displaystyle 3}}{{\displaystyle 2^n}}}}{{\displaystyle \frac{{\displaystyle 1}}{{\displaystyle 2^n}}-1}}=-1. \end{gathered}$$;