I'm pretty sure those are to see your preference to see your interest on the application... Also, I believe they are short presentations (like classes) to let you get the feel of the classes and what that field is like
Congratulations!!! I'm attending Session C too, but I also applied to USNA summer seminar. Although that's a tough decision to make, regardless you are going to have a wonderful experience because I have friends who attended either one and they have all come back with great stories to share!