On each horizontal line in the figure below, the five large dots indicate the populations of cities $A, B, C, D$ and $E$ in the year indicated. 
Which city had the greatest percentage increase in population from $1970$ to $1980$?
$\textbf{(A)}\ A\qquad \textbf{(B)}\ B\qquad \textbf{(C)}\ C\qquad \textbf{(D)}\ D\qquad \textbf{(E)}\ E$
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 $\boxed{\text{C}}$.