单选题 The millions of calculations involved, had they been done by hand,______all practical value by the time they were finished.

A、 could lose
B、 would have lost
C、 might lose
D、 ought to have lost

【正确答案】 B

【答案解析】解析：句意：如果人工计算，等到结果出来的时候，这数百万的计算步骤也就失去意义了。此处“had they been done by hand”相当于“If they had been done by hand”，用的是过去完成时，表示与过去事实相反的假设，因此主句须用过去将来完成时。