问题
选择题
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
答案
Ａ
by+过去时间，谓语用过去
完成时态。
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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
Ａ
by+过去时间，谓语用过去完成时态。