P(p) and Q(q) are the position vector of two fixed points and R(r) is the position vector of a variable point. If R moves such that (r−p)×(r−q)=0 , then the locus of R is
(1) a plane containing the origin O and parallel to two non-collinear vector OP and OQ .
(2) the surface of a sphere described on PQ as its diameter.
(3) a line passing through the points P and Q .
(4) a set of lines parallel to the line PQ .