听力原文：M: Can you tell me about the university shuttle bus system？ This is such a large

campus, and I have classes all over it. I need to take the shuttle bus from one class to another, or I will never make it on time.

W: What do you need to know？ I think it's a really great system.

M: First of all, where does it go？

W: The university shuttle bus goes all over campus. It does not leave the campus; if you want to travel off-campus, you'll need to take the city bus. But the university shuttle bus will get you from one class to the next, very efficiently.

M: And how much does it cost？

W: It's free, can you believe it？ So you don't have to pay a cent to get all around the university campus.

M: That's really great. And how do I catch the shuttle bus？

W: Just look for one of the bright yellow shuttle bus signs, and go stand next to it. You can see the shuttle bus signs all over campus. A shuttle bus will come along approximately every five minutes, so you shouldn't have to wait long.

M: That all sounds good. Thanks for your help.

W: No problem.

What are the man and woman discussing？

A．The size of the campus.

B．The city bus system.

C．The school bus system.

D．The differences between two bus systems.