5-9  Please be quiet. 

Please be quiet.   Please keep it down.   Could you lower your voice? You're too loud.   You're too noisy.   You're disturbing everybody.   Sorry to say that. I hope you don't mind.    Please don't take offense.
 

5-9 请安静一点。

说话请小声一点。你能不能把声音降低一点？你太大声了。你太吵了。你打扰到大家了。很抱歉我那么说。我希望你不要介意。请不要生气。