He made another wonderful discovery, of great importance to science.
A. which I think it is
B. which I think is
C. which I think
D. I think which is
网友回答
A. which I think it is
(答案→)B. which I think is
C. which I think
D. I think which is
解析：考查插入语：句意：他做出了一个重大发现，我认为这对科学是非常重要的，which引导的是非限制性定语从句，I think是插入语，在which后面，去掉I think可知which是定语从句的主语，it是多余的，选B。