Mark Twain school and began to work at the age of twelve.A. leftB. leavesC. will leaveD.

问题补充：

Mark Twain school and began to work at the age of twelve.

A. left

B. leaves

C. will leave

D. leave

答案：

(答案→)A. left

B. leaves

C. will leave

D. leave

解析：句意：在十二岁的时候，马克吐温离开了学校，开始工作。结合语境可知本句描述的是过去某时发生的动作，故用一般过去时态，选A。