By the time he was ten,Edison______experiments in chemistry.A.had already doneB.already had doneC.wa

题目简介

By the time he was ten,Edison______experiments in chemistry.A.had already doneB.already had doneC.wa

题目详情

By the time he was ten,Edison______experiments in chemistry.
A.had already done    B.already had done
C.was already doing    D.already did
题型:单选题难度:偏易来源:不详

答案

by+过去时间,谓语用过去完成时态。

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