根据语境，用恰当的语言完成对话。

A: Good morning, Mary.

B: Good morning, Helen. Come in, please.

A: Thank you. Your room is very nice. Oh! A bookshelf and many books. 1______

B: Thank you. I like reading, you know. I think reading can make a person wise.

A: Did you do well in the English exam?

B: Yes. I just learned I passed the English exam and the result is good. I have got an "A".

A: 2______ 

B: Thank you. 3______  Why?

A: We will have a math exam next Monday. I'm afraid I may fail the exam. So I've come for some help.

B: Don't worry. 4______ 

A: That's great. Thank you very much.

B: 5______  A friend in need is a friend indeed.

A: That's true. When shall we start?

B: Right now.

泵的有效功率永远（）轴功率。

A、小于

B、等于

C、大于