If vector(a,b,c) are three non-coplanar vectors and vector(p,q,r) are defined by the relations vector p = vector(b x c)/vector[a,b,c], vector q = vector(c x a)/vector[a,b,c], vector r = vector(a x b)/vector[a,b,c], then vector(p.(a + b)) + vector(q.(b + c)) + vector(r(c + a)) = ...
(a) 0
(b) 1
(c) 2
(d) 3