Introduction to class, system safety, and hazard identification (PDF).
课程介绍，系统安全，和危险确认(PDF)。
The Introduction to Economics class is so lame!
经济学导论可真差劲！
I'm very glad to have an introduction at the beginning of the class.
一开始上课，我很高兴做一下介绍。
I'm very glad to have an introduction at the beginning of the class.
一开始上课，我很高兴做一下介绍。
应用推荐