单选题
Much labor would have been saved if the electronic computers ______ before.
A、
had invented
B、
were invented
C、
should have been invented
D、
had been invented
【正确答案】
D
【答案解析】
[解析] 本题考查虚拟语气的用法。根据主句中的“would have been saved”可知从句应用过去完成时表示与过去相反的假设。故答案为D。
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