smc

We simply have to divide the present population by the original, and whichever one is the largest have the greatest percent change. City $\text{A}$ is $\frac{50}{40}=1.25$. City $\text{B}$ is $\frac{70}{50}=1.4$. City $\text{C}$ is $\frac{100}{70}\approx 1.42$. City $\text{D}$ is $\frac{130}{100}=1.3$. City $\text{E}$ is $\frac{160}{120}\approx 1.33$. City $\text{C}$ has the greatest value, so the answer is $\boxed{C}$.