Question

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

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

Answer 1

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
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。