题目

He has made another wonderful discovery,___ of great importance to science.        A. who I think it   B.which I think it is   C. that I think is   D. which I think is 答案：D 解析: 首先去掉插入语I think，使选项明朗化；因前后都是两个无连词的句子，可判断后句为非限制性定语从句。

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