If A = (p, q, r) and B = (p′, q′ r′) are two points on the line λx = μy = γz, such that OA = 3, OB = 4, then pp′ + qq′ + rr′ is equal to
(A) 7
(B) 12
(C) 5
(D) of these
Answer is (B) 12
