16.He would have given you more help， if he ________ so busy.
A. have not been
B. had not been
C. not have been
D. not had been
17.After months of voyage， Columbus arrived in ______ later proved to be a new continent.
A. where
B. which
C. what
D. that
18.I was really anxious about you. You ______ home without a word.
A. mustn‘t leave
B. shouldn’t have left
C. couldn‘t have left
D. needn’t leave
19.He was ______ to withdraw from running for the presidency.
A. trusted
B. credited
C. convinced
D. believed
20.While _____ the book， he nodded from time to time
A. reading
B. read
C. is reading
D. is read
