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

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. was begun

答案：

A. would begin

B. has begun

(答案→)C. had begun

D. was begun

解析：时态题。By the time +过去时，主句谓语用过去完成时态 选C。 句意：到爱迪生十二岁时他已开始自己谋生了。