The two lines $x = ay + b, \; z = cy + d$ and $x = a' y + b', \; z = c' y + d'$ will be perpendicular, if and only if :

Question

( A ) $aa' + bb' + cc' = 0$
( B ) $aa' + bb' + cc' + 1 = 0$
( C ) $aa' + cc' + 1 =0$
( D ) $(a+a') (b+b') + (c + c') = 0$