题目

20. It was quite a serious accident, _____caused by careless driving. A. which I think was   B. I think which was C. which I think it was  D. I think which it was 答案：A 解析: 选A。本题考查由which引导的非限制性定语从句，which替代先行词accident 在定语从句中作主语。I think 是插入语，放在which后面。