用恰当的词语填空，完成对话。每空一词。

A: Good morning, sir! Can I 1______ you?

B: I would like to buy an MP4.

A: Here is a new kind. Please have a 2______

B: OK. Let me try to listen to it.

A: Is it loud and clear enough?

B: Yes, it is. But I don't like black. Have you got a red one or a white one?

A: Yes. How about this red one?

B: It's nice. How 3______ is it?

A: 300 yuan. Is it OK?

B: Oh, dear! That's too expensive. Can it be 4______?

A: You can pay 50 yuan less. That's the last price.

B: OK. I'll 5________ it. Here's the money.

日本血吸虫的最严重的病变主要由下列何者所致()

A．成虫

B．尾蚴

C．毛蚴

D．童虫

E．虫卵