_____, many problems of space flight could not be solved now.
A、
If electronic computers would not have been invented
B、
Had electronic computers not invented
C、
Had electronic computers not been invented
D、
If electronic computers were not invented
【正确答案】
C
【答案解析】
解析：此句为混合型虚拟语气结构，从句表示与过去事实相反，主句是表示与现在事实相反。省去if，虚拟条件状语从句用倒装形式，故C正确。
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