Answer
$\textbf{(a)}$ It is greater.
$\textbf{(b)}$ The best explanation is $\textbf{II}$.
Work Step by Step
$\textbf{(a)}$ It is greater than that of the driver $1$. Namely, since they fall from the same height, the vertical components of their velocities would be of the same magnitude, but driver $2$ also has a constant horizontal component so the final, splashdown, speed will be bigger in his case.
$\textbf{(b)}$ The explanation that is in accord with the part $\textbf{(a)}$ is $\textbf{II}$.
