Let $P$ be a point on the parabola $y ^ { 2 } = 4 a x$, where $a > 0$. The normal to the parabola at $P$ meets the $x$-axis at a point $Q$. The area of the triangle $P F Q$, where $F$ is the focus of the parabola, is 120. If the slope $m$ of the normal and $a$ are both positive integers, then the pair $( a , m )$ is
(A) $( 2,3 )$
(B) $( 1,3 )$
(C) $( 2,4 )$
(D) $( 3,4 )$