# If the pair of straight line $x^2 -2pxy - y^2 = 0$ and $x^2 - 2qxy - y^2 = 0$ be such that each pair bisects the angle between the other pair, then :
( A ) $pq = 1$
( B ) $p=q$
( C ) $p = -q$
( D ) $pq = -1$