74.should/ought to have done… 本应当做某事但没做
75.shouldn't have done…/oughtn't to have done… 本不应当做某事但做了
76.sb be familiar with sth/sth be familiar to sb 熟悉
77.be able to do…/enable sb to do… 能够做某事/使某人能做某事
78.it is time… 到……的时间了
79. by the time… 到……的时间前
80.happen/happen to do… 发生/碰巧做某事
