Answer:
Say NO to ALL of them.
Explanation:
Decline the offer of a cigarette but sit them down and explain that cigarettes will slowly kill them and that you don't want them to die because they are one of your closest friends.
Call the cops on the party for underage consumption of alcohol.
Report the student for handling marijuana, especially since in a lot of places it's still illegal.
Eventually stage an intervention for your drug addict friend, or at least call her some help if all else fails.
