You have to read the book before. To make understand.
You have to read the book before, to make it easier to understand the more quickly.
you should enter a classroom for about 10-20 minutes
you should enter the classroom before about 10-20 minutes
You should attend classes before the approximately 10-20 minutes
After that, when the teacher arrives, you must stop the talk and do not make noise disturbing others.
you should not bring a snack to eat between classes
you should attend classes and deliver on time every time.