问题: 作业求助 英语单选
the millions of calculations involved,__ by hand ,would have lost all practical value by the time they were finished.
a.had they been done
b.they had been done
c.having been done
d.they were done
解答:
答案选A。
这是一个带有对过去事件假设的虚拟语气的句子，而且用了省略倒装结构。
句意：如果有关的大量计算用手工完成，那么到完成之时这些计算结果会失去其使用价值，变得毫无实际意义。
had they been done = if they had been done
这个时态结构和would have lost是相对应的。
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