By the time he was twelve, Edison _______ to make a living by himself.A．would be

题型：不详难度：来源：

By the time he was twelve, Edison _______ to make a living by himself.

A．would begin

B．has begun

C．had begun

D．began

答案

C

解析

试题分析：考查时态。By…到…为止；与完成时连用。后面接the time he was twelve是过去时，故主句中使用过去完成时。句意：到他12岁的时候，Edison已经开始靠自己谋生了。故C正确。
点评：时态题中对by的考查是最关键的，by到…时为止；与完成时连用。