$[2$ points$]$ Consider Java's dynamic data structure java.util.ArrayList. It automatically doubles its size when it's full and halves its size when less than one$-$quarter of the cells are filled with data. For each of the following operations, identify its running time by the following listed orderof$-$growth term. Assume $n$ is the original input data size.

A: $O(1)$

B: $O(logn)$

C: $O(n)$

D: $O(nlogn)$

E: $O(n^2),$ F: $O(n^3)$

$5\mathrm{.}1)$ Return the element at index $\frac{n}{2}$ in the list.