题干
阅读对话，回答问题。
Sue: Hello, I want to buy some pingpong balls. Can you help me?
Clerk: Sure. Do you like these balls or those balls?
Sue: I like these balls. How much are they?
Clerk: They're 2 dollars each.
Sue: I need three pingpong balls.
Clerk: OK. Here they are.
Sue: Thank you.
Clerk: You're welcome.
