The millions of calculations involved, ______by hand, would have lost all practical value by the time they were finished.

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问题 The millions of calculations involved, ______by hand, would have lost all practical value by the time they were finished.

选项 A、had they been done
B、they had been done
C、having been done
D、they were done

答案A

解析 本题考查虚拟语气。虚拟语气表示与过去事实相反的情况,主句用would have done,从句用had done。如果省略引导非真实条件句中的引导词if,助动词had应提前,故答案为[A]项。
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