A. Fifteen books.    
B. Yes, I have fifteen books.

(     )1. Can I help you?
(     )2. How much is it?
(     )3. What colour is it?
(     )4.Is it cheap?
(     )5. How many books do you have?
A. It's ten yuan.
B. No, it's expensive.
C. Fifteen.
D. Yes.
E. It's yellow.