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.