I tried to _________them down to their promise, but I failed.
A. ask
B. tell
C. nail
D. knock
Nobody but Jack and Tom ________ in the office yesterday.
A. are
B. was
C. were
D. have been
They nodded ________each other in greeting.
A. to
B. for
C. in
D. up
Li Lei didn't meet the famous American professor ________ he was on holiday in American last year.
A. unless
B. until
C. if
D. whether