如果a×b=0,那么请选择ABCD.r+Y'y;[.Q,k9i*M'y5a2a3t
A.a一定等于0'y5a2a3t
B.b一定等于0'y5a2a3t
C.a和b都等于0'y5a2a3t
D.a和b至少有一个等于0'y5a2a3t