解答：选（D）该题第一句是陈述事实，可以分析第二句应使用虚拟语气且应为与过去事实相反的假设，所以使用should have done的形式。同时在该句还应使用被动语态形式，所以该句的句式为should have been done。

22. We could not have fulfilled the task in time if it _________ for their help.

   A. was not     B. is not       C. had not been    D. has not been

解答：选（C）该题考查虚拟语气的用法，表示与过去事实相反的假设，句式结构为：If + 主语 + had + 过去分词，主语 + would / might + have + 过去分词。例如：If the pilot hadn’t dealt calmly with the accident, we wouldn’t have survived.要不是飞行员沉着冷静地处理意外，我们就不可能幸免于难。

23. The hotel ________ during the vacation was rather poorly managed.

   A. as I stayed    B. where I stayed    C. which I stayed    D. what I stayed

解答：选（B）本题的先行词是表示地点的词，应用where引导的从句修饰限定，the hotel where I stayed相当于the hotel at which I stayed或者the hotel I stayed at。Stay为不及物动词，应加介词at，再加宾语，所以C项也可改为at which I stayed或which I stayed at，均为正确选项。

24. I stayed up all night ______ to find a new solution to the problem.

   A. trying   B. have tried   C. try     D. tried

解答：选（A）

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