请将短文翻译成汉语。
Professors may establish social relationships with students outside of the classroom, but in the classroom they play the role of an instructor. A professor may have coffee with students one day but the next day he may expect them to meet a deadline for a paper or to be prepared for a discussion or an exam. The professor may give extra attention, outside of class, to a student in need of help, but probably will not treat him or her differently when it comes to evaluating academic work. Professors have several roles in relation to students; they may be counselors and friends as well as teachers. Students must realize that when a teacher's role changes, they should change their behavior and attitude accordingly.