【题目】He has made a discovery, _________ of great importance to the progress of science and technology．
A．I think which is B．which I think is
C．which I think it D．which I think it is
在线课程【答案】B
【解析】
试题分析：考查定语从句。句意：他做了一个调查，这个调查我认为它是很重要的对于科学技术的提高。非限制性定语从句which在句首，which做主语，不加it，根据句意知选B。