Once environmental damage_____, it takes hundreds of years for the system to recover.

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问题 Once environmental damage_____, it takes hundreds of years for the system to recover.

选项 A、has done
B、is to do
C、does
D、is done

答案D

解析 本题综合考查动词的时态和语态。句中主句的谓语动词takes用的是一般现在时,根据条件从句中时态的替代,从句中也应该用一般现在时表将来时,由于主语是envi—ronmental damage,所以谓语动词要用被动语态。
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