Which of the following perceptions influence why and how people drink: a) how much we think others are drinking b) how often we think others are drinking c) what we think we will or won't get from drinking d) all of the above

The answer is D - all of the above.

There are many reasons why people drink when they do or how much they do. The perceptions listed above are all possible reasons why as a lot of how we think and act are the result of societal pressures or expectations from other people and ourselves.  

9, 5, 10000000 ( that is supposed to be a ten for the last one)