The National Association for Sport and Physical Education says twenty to thirty students in a P.E.class should be the limit.

VOA: special.2009.08.06

c p 1 points to an instance, it points to a particular version of this class.

奇怪形式的句子，不是那么奇怪,你们以前也见过这样的。

麻省理工公开课 - 计算机科学及编程导论课程节选

But other days I'll have class from 10 a.m to 6 p.m.

但是其他时候，我会从早晨十点一直上课到下午六点。

很好奇住宿生活 - SpeakingMax英语口语达人