Scientific research indicates that two-thirds of the earth's surface ______ with water.
A.covered
B.are covered
C.covers
D.is covered

A.A.covered
B.are
B.covers
D.is

【参考答案】

D
解析：该题考查考生对主谓一致以及被动语态的掌握。地球三分之二的表面是个单数概念，所以要用第三人称单数；同时，......

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