—No , you ________. It is not as serious as the one we went to last week .
A:mustn't
B:needn't
C:can't
D:wouldn't
74+19=____
对于全集U的子集M,N,若M是N的真子集,则下列集合中必为空集的是( )
已知x3=y2,那么下列式子中一定成立的是( )