We use Snell's equation

$\begin{align*}1.33 \sin \theta_1 = \sin \theta_2\end{align*}$
where $\theta_1$ is the angle the the light makes with the normal below the surface of the water and $\theta_2$ is the angle that the light makes with the normal above the water. The maximum value of $\sin \theta_2$ is $1$ , so total internal reflection occurs when

$\begin{align*}\theta_1 = \sin^{-1} \left(1/1.33\right) = \boxed{48.75^{\circ}}\end{align*}$
Therefore, answer (C) is correct.

Solution to 1996 Problem 56