A、The assistants must know their names. B、They tell what their majors are. C、Too many non-students use the lab. D、The computers

Hi, I’d like to welcome you all to the computer lab orientation.
    We’ll be going into the main lab in a moment, but I want to direct your attention to the bulletin board here in the hallway first. The hours and locations for several other labs are posted on this board. These other labs can be found throughout the campus, but they are all considerably smaller than the main lab. Most of the larger departments have their own computer labs which give priority to students who are departmental majors during times of heavy usage. You will probably want to take note of this information because during midterms and finals we occasionally have large lists of students waiting to use the computer terminals.
    In general, there are several rules that apply to computer usage across the campus. The first and foremost rule is that no food or drinks are permitted in any computer lab at any time. The first offense will earn you a warning and the second time you will be asked to leave the lab. The second rule is that you must place your student identification card in the holder next to the computer. This second rule is necessary because we’ ve had so many non-students using the facilities and we really don’t have enough machines for the students, much less the population at large.
Questions 21-25 are based on the passage you have just heard.
21. Where is the speaker most probably speaking?
22. What is the primary purpose of the talk?
23. What advantage does the speaker mention about other labs?
24. What is the most important rule in the computer lab?
25. Why do students need to display their identification cards?