in class还是on class

　　in class，指地点比较合适。someone is in class。相当于someone is in classroom.

　　on class，指时间比较合适。someone is on class.相当于someone is busy, not free, is on class.

　　例句：

　　Does the quality of teaching depend on class size?

　　教学质量取决于每个班的人数吗？

　　He has already caused apoplexy with his books on class and on war.

　　他关于阶级和战争的书已经激起了极大的愤怒。

　　She keeps good discipline in class.

　　她严格执行课堂纪律。

　　She was admonished for chewing gum in class.

　　她在课堂上嚼口香糖，受到了告诫。