By the time he was twelve Edison to make a living by himself.A. would beginB. has begunC

问题补充：

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：

A. would begin

B. has begun

(答案→)C. had begun

D. began

解析：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。