The split between humans and living apes is thought by some scholars ____ 15 to 20 million years ago.A.to occurB.occurringC.to have occurredD.having occurred
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C解析本题考查非谓语动词。 be thought to do“被认为做某事”，因为后边是 15 to 20 million years ago 已经发生了，因此用不定式的完成式。