--Are you a teacher?No but I .A. used toB. was used toC. used to beD. used to do

问题补充：

--Are you a teacher?

--No, but I .

A. used to

B. was used to

C. used to be

D. used to do

答案：

(答案→)A. used to

B. was used to

C. used to be

D. used to do

解析：考查不定式的省略式：英语的不定式的动词上文出现过的话，可以省略to后面的动词，但是be动词或have一般不省，句意：--你是老师吗？--不是，但过去是的，选A。