If $f(x)=x^2+5x+p$ and $Q(x)=x^2+3x+q$ have a common factor, then the common factor is

Question

$\begin{array}{1 1} (a)\; p-q \\ (b)\; q-p \\(c)\; \frac{p-q}{2} \\ (d)\; \frac{q-p}{2} \end{array}$