单项选择题

M: Jone, do you want to go swimming with me today
W: Sure. But I can’t leave now. I have an appointment with my professor at three o’clock.

Why can’t Jone go swimming now()

A. He must meet his teacher.
B. He must attend a class.
C. He must go out with his girlfriend.
D. He must stay at school to finish his homework.