单选题
The millions of calculations (involved) , (had they) been done by hand, would (lose) all practical value (by the time) they were finished.
A、
involved
B、
had they
C、
lose all
D、
by the time
【正确答案】
C
【答案解析】
改为have lost。had they been done是对过去情况的虚拟，主句结构应用would have done。
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