Can you help me with a university housing application?

I was recently accepted to a university for summer. I am applying for student housing and it asks which summer session I am applying for (A, B, or C). The problem is that I don't know which session I am going to attend, my orientation is in a month and that's when I will enroll in classes. Should I just pick the one I think I will attend and apply now or should I wait? What's weird is that the website says to apply as soon as you are accepted, it just doesn't make sense because I haven't enrolled yet. I'm just worried that if I wait I might not get housing. :( Please help!