— Are you a teacher? — No but I . I worked in a middle school for three years.A. amB. wil

问题补充：

— Are you a teacher?

— No, but I . I worked in a middle school for three years.

A. am

B. will

C. do

D. was

答案：

A. am

B. will

C. do

(答案→)D. was

解析：这里用was表示说话者过去是老师。这与整个题干以及提供的情境相符合。