题目内容：

In western countries, people like to keep quiet when they are in public. If there is someone talking and laughing loudly in a restaurant, the waiter will stop him at once .Which fits the western customs?

A．a : Sorry, sir. You have to speak in a low voice.b: What? It’s just my case

B．a: You shouldn’t speak so loudly. Or you must go away.b: Sorry ,I won’t do that again

C．a: Excuse me, please speak in a low voice.b: I’m sorry for that. I won’t do that again.