If $a \cot \theta + b\; cosec \theta =p$ and $b \cot \theta + a\; cosec \theta =q ,$ then $p^2-q^2=$

Question

$\begin{array}{1 1}(A) \; a^2-b^2 \\(B)\; b^2-a^2 \\(C)\;a^2+b^2 \\(D)\;b-a \end{array}$