The defense works_________long ago to ke

tikufree2019-12-17  9

问题 The defense works_________long ago to keep the enemy away.

选项 A.were builtB.has been builtC.had been builtD.was built

答案D

解析考查动词时态和主谓一致。主语The defense works(防御工程)是集合名词,当成整体考虑,谓语动词要用第三人称单数形式。long ago表示过去的时间,所以用一般过去时态的被动语态。故选D。
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