By the time he was twelve, Edison _________

试题详情及答案解析

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

A．would begin	B．has begun
C．had begun	D．was begun

答案：C

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。
考点：考查时态