If the pair of straight lines $x^2-2pxy-y^2=0$ and $x^2-2qxy-y^2=0$ be such that each pair bisects the angle between the other pair then,
$\begin{array}{1 1}(A)\;pq=-1 \\(B)\;p=q \\(C)\;p=-q\\(D)\;pq=1 \end{array}$