He made another wonderful discovery, ________ of great importance to science.
A.which I think is
B.which I think it is
C.which I think it
D.I think which is
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A解析这是一个非限制性定语从句，make another wonderful discovery是动宾词组，关系代词which在定语从句中作主语，代表the discovery, I think为插入语．