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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【S1】[br]【S2】them→it一致问题。此处them指的是前面的alivingcell，属于单数，因此应当改为it。