In your opinion, how do alcohol advertisements build pleasant expectations about consuming alcohol? how can this affect the behavior of some adolescent viewers?

In my opinion, they build pleasant expectations bout alcohol by always showing people having a good time by consuming it. You never see an alcohol commercial where the people are not enjoying themselves. 
This can affect younger people because when they see on TV that it does no harm to the adults, they think it won't do anything to them. They are going to want to try it, because all they see is people having a good time while drinking. 

Hope this helps!