第19题: [单项选择]They overcame all the difficulties and completed the project two months ahead of time, ______ is something we had not expected. A. which B. it C. that D. what 参考答案:A 答案解析:本题译文:他们克服了所有的困难,提前两个月完成这项工程,这是我们没料想到的。此题是非限制性定语从句,选项中只有which可以用于这种从句,这里which代替前面的所有内容。