A.1/2 B.1/4 C.1/8 D.1/3
A.(a×b)×(c×d) B.{(a×b)×c}×d C.(a×b)×(a×c) D.a×b×c×d
A.a×b×c B.(a×c)×b C.(a×b)×c D.(b×c)×a