根据上下文选择合适的句子把对话补充完整

A. No, it isn't           B. Forty        C. Yes, we do   D. Is this the art room    E. It's so big

A: Welcome to our school! This is my classroom.

B: . How many students are there in your class?

A: .

B: Is that the music room?

A: . It's the computer room.

B:?

A: Yes, it is.

B: Do you have a library?

A:. It's on the second floor. This way, please.