问题
选择题
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
答案：D
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。