Tuition, faculty, location, reputation. I see you dropped a class. Be careful not to say bad things about the professor. Take the responsibility, even if the prof was a jerk-never ever forget that the interviewers are often the faculty of the program. Unless you have a 4.0, say yes.
Brief explanations are acceptable but they all end up sounding lame.
I had all As. My best friend gave my favorite answer to this one. He said that he knew they wanted good graduates who would make them proud and he said he wouldn't let them down. They loved it. He got in his first try.