The astronaut did many experiments in the spaceship, great help for knowing more about space.A.which we think it isB.which we think is ofC.of which we think isD.we think which is of
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B解析考查非限制性定语从句。句意“那位宇航员在太空船上做了许多实验，我们认为这些实验对更多地了解太空很有帮助。”句中有逗号，是非限制性定语从句，be of+抽象名词，相当于对应的形容词，例如：be of help=helpful；be of importance=important。故选B。