I feel that one of my main duties ________ a teacher is to help the students to become better learne

I feel that one of my main duties ________ a teacher is to help the students to become better learners．

A.for

B.by

C.as

D.with

答案及解析： C

解析：

as a teacher在此表示“作为一名教师”，其他选项无此含义。