Had electronic computers not been invented, ______ (很多关于太空飞行的问题不能解决了). many prob

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问题 Had electronic computers not been invented, ______ (很多关于太空飞行的问题不能解决了).

选项

答案 many problems of space flight could not have been solved

解析 (if从句中的had移到句首后,if省略了,从句中依旧用否定式的could not have been solved;被动语态构成为have been done)
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