六淫致病的一般特点不包括
A．季节性与地域性
B．单一性与相兼性
C．不变性
D．转化性
E．外人性
参考答案：C
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
