题目

Astronomers estimate        called the Pleiades in the constellation Taurus is 415 lightyears away from Earth. A.that a loose cluster of stars      B.a loose cluster of stars is  C.that is a loose cluster of stars      D.there is a loose cluster of stars 答案： A estimate是及物动词，后面的空格应该是宾语，或者宾语从句。A项从句的谓语是后面的is。B、C、D三项的谓语和后面的谓语矛盾了，一个句子只能有一个谓语。

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