Ans: A
Let $R(h,k)$ be the orthocentre of $\Delta OPQ$. Note that $OP$ is lying on the $y$-axis and $OP\perp RQ$. Therefore, $RQ$ must be parallel to the $x$-axis, then $k=48$. Since $PQ \perp OQ$, then we have
$\begin{array}{rcl}
m_{PR} \times m_{OQ} & = & -1 \\
\dfrac{60-48}{0-h} \times \dfrac{48-0}{96-0} & = & -1 \\
\dfrac{12}{-h} \times \dfrac{1}{2} & = & -1 \\
h & = & 6
\end{array}$
