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单选题
276.Some martian rock structures look strikingly like structures on Earth that are known _________ by microbes.
A
having been created
B
being created
C
to have been created
D
to be created
答案解析
正确答案：C
解析：
解析:空格所在的定语从句为 sth. be known to do 结构;that 指代地球上的岩石结构,与 created 之间存在被动关系;当不定式动作发生在谓语动词的动作之前时,不定式需要用 完成式。即:在人们知道之前,岩石结构已经由微生物创造成,即 created 动作发生在 are known 之前,所以选择 to have been created。 句意:一些火星的岩石结构看起来跟地球上 的岩石结构极为类似。人们已知,地球上的岩石结构是由微生物创造的。
相关知识点：
be known to have done
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