799.Peter _______ be really difficult at times even though he's a nice person in general.
A.shall
B.should
C.can
D.must
800.I'm sorry.I _____ at you the other day.
Forget it.I was a bit out of control myself.
A.shouldn't shout
B.shouldn't have shouted
C.mustn't shout
D.mustn't have shouted
799.答案是C;表示客观的可能性。
800.答案是B; shouldn't have done sth.,本不应该做某事而实际上已经做了。
