A、The size of the campus. B、The city bus system. C、The length of time for each class. D、The university bus system. D选项全是名词短语，问对话

M: [12]Can you tell me something about the university shuttle bus system? This is such a large campus, and I have classes all over campus. I need to take the shuttle bus from one class to another, or I’ll 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: [13]The university shuttle bus system goes all over campus. It doesn’t leave the campus; if you want to travel off-campus, you’ll need to take the city bus system. But the university shuttle bus system will get you from one class to the next very efficiently.
M: And how much does it cost?
W: [14]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: [15]Just look for one of the bright yellow shuttle bus signs, and go stand next to it. You can see the yellow 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.
12. What are the man and woman discussing?
13. What area does the university shuttle bus cover?
14. How much does the shuttle bus cost?
15. What color are the shuttle bus signs?