I have to______my visit as I' 11 be very busy next week.
A. call for
B. call on
C. call off
D. call in
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______ how to operate a switchboard, I had to ask the office supervisor to show me the correct procedures.
A. Not known
B. No to know
C. Not knowing
D. Having not known
It's already five o' clock now. Don't you think it's about time______？
A. we are going home
B. we go home
C. we went home
D. we can go home
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