肛门内括约肌的主要生理作用是（）
A.括约肛门
B.防止脱垂
C.帮助排便
D.载托盆腔
E.保持肛门外形
参考答案：C
— I've decided to go back to school for some training in programming.
— . When would you like to start?
A．Good for you
B．Up to you
C．You can have it
D．I got you
除尘器的类型有哪些？
