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

16.正確答案：B答案解析：本題考察與過去事實相反的虛擬語氣。

17.正確答案：C答案解析：注意，本句話并非定語從句，而是賓語從句。因為在介詞in 后面，應該用what引導的賓語從句，what在賓語從句中作主語。

18.正確答案：B答案解析：虛擬語氣用法。句意：我(那時)真的很擔心你。你本不應該不留個話就離開家。

19.正確答案：C答案解析：句意：他被說服退出競選總統。convince使相信;信服;說服。

20.正確答案：A答案解析：從句中動作的發出者和主句相同，用現在分詞短語作時間狀語。題意為：他一邊看書，一邊不時地點頭。

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