4. 若 A = [aij ]m×n, B = [bij ]n×p, C = [cij ]n×p 及零矩陣 O, 則下列敘述何者正確?
(A) AB + AC = A(B + C)
(B) 若 AB = O, 則 A = O 或 B = O
(C) 若 AB = AC 且 detA 6= 0, 則 B = C
(D) (AB)2 = A2B2
(E) AB = BA