66、 My wallet is nowhere to be found．I______ when l was on the bus
A．must drop it
B．should have dropped it
C．must have dropped it
D．had dropped it


67、
He_________ reading silently at first.
A．used not to
B．didn' t use to
C．was not used to
D．is not used


68、 You can’t hear what I’m saying______you stop talking
A．only if
B．unless
C．lest
D．except that


69、 Babies often_________ down when they are learning to walk.
A．drop
B．fail
C．slip
D．jump


70、 ________anything about the accident, he went to work as well.
A．Not know
B．Know not
C．Knowing not
D．Not knowing


71、 It is necessary that we________ have a good command of English at college.
A．must
B．have to
C．should
D．ought to


72、They discussed the problem three or four times, but could come to no _________
A．end
B．conclusion
C．result
D．judgment


73、In some countries_________ are getting richer and richer.
A．rich
B．the rich
C．riches.
D．the riches

74、 ________the traffic jam, we would have caught our train.
A．But for
B．Because of
C．By means of
D．Due to


75、
It was not_________1982 that he went back to America.
A．since
B．until
C．before
D．after