The millions of calculations needed, had they been done by hand, ________ all practical value by the time they were finished．A.had lostB.would loseC.would have lostD.should have lost
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C解析句意：如果人工进行包含数百万次的计算，等结果出来，它也失去了价值。由于从句中省略了if，故而助动词提前，与过去事实相反，所以选C项。