B, with a hint of A. As med students, I’m assuming you guys get crushed studying-wise fairly often. Chances are he actually was busy. Maybe he got slammed at the last minute. Also, the fact that your plans weren’t concrete makes me think he felt like he could cancel if he needed to study.
However, there are two things that make me think he might not be 100% interested. First, he told you to call him to make plans. I’m all for women taking the initiative and asking a guy out, but when the guy leaves it to you to make a move, it’s often an indication of his level of interest. Also, he didn’t call you to cancel– he just let you do everything. If I was interested in someone and had to cancel, I would call, be extremely apologetic, and hope that I get a second chance. At the very least, an email letting you know that he was going to have to cancel would show that he really does want to hang out and regrets being busy.
That’s not to say he isn’t interested. But his level of effort so far suggests that you might not be a priority. Which is okay– perhaps he needs to hang out with you and get to know you better. And, again, I would give him the benefit of the doubt that he was telling you the truth considering that you’re both busy med students. Give him another chance, but let him do the planning. You made the effort, and he was busy. If you want confirmation that he’s interested in you, let him make the next move. That way, you’ll be pulling a “C” and playing a little hard to get. That move never fails.