语法与词汇 They overcame all the difficulties and completed the project two months ahead of time,_____ is something we had not expected.
【正确答案】 A
【答案解析】句意：他们克服了所有的困难，提前两个月完成了任务，这是我们没有想到的。定语从句，which指代前文交代的事情。