Which of the following perceptions influence why and how people drink:

I believe that all of the above influence why and how people drink: how much we think others are drinking, movies and advertisements, and family upbringing.
If you see that your friends are drinking a lot, you (especially if you are an impressionable teen) will want to drink a lot too; movies can also influence you either to drink a lot or to stay away from drinks, as well as how you were raised. 

3. i would say one, but one is not prime nor composite.