题目内容：

Last year there were many problems which____by bad weather A.caused B.was caused C.were caused

优质解答

答案：C.were caused .
分析：Last year there were many problems which were caused by bad weather.
去年有很多因为气候引起的问题.which were caused =caused.

追问：

why - -?

追答：

已经修改了，嗯。which引出定语，没有which的话选A.caused 。