Possible answers:
(I). They're your friends and they'll still be there after the lecture/class/tutorial. In fact, they might start getting on your nerves if they're around too much over-analyzing all the work in front of all of you.
(II). Although these people know you well, they may still ask probing questions about how you're doing. Talking to fellow students is a good way to have a conversation, but avoid asking them about their daily activities and personal lives.
(III). They may feel sad, surprised or, most likely, angered because you have moved on. If you do befriend them, try not to talk about your feelings unless you are asked.
(IV). Your friends will see that you have trouble focusing. If they'll notice, they might try to exploit your small talk with them.Choose from options above and answer: What most naturally follows?

How to concentrate at university level classes 
Avoid talking to strangers during lectures and tutorials. 
While it might be nice meeting new people and discovering their interests, there are better times for doing this than during teaching sessions when you need to be concentrating. 
Avoid talking to your friends.
Answer:
(I).