Since teaching is a job no one can be perfect at, it is necessary for teachers to keep improving their knowledge of the subjects they teach and their ______.

证券发行和交易必须遵循的原则包括（）

Ⅰ.公开原则

Ⅱ.公平原则

Ⅲ.自愿原则

Ⅳ.公正原则

A.Ⅰ、Ⅱ、Ⅲ

B.Ⅰ、Ⅱ、Ⅳ

C.Ⅰ、Ⅲ、Ⅳ

D.Ⅰ、Ⅱ、Ⅲ、Ⅳ