Buy a MP4
买了个MP4

May I help you?
能帮您忙吗？
I bought the MP4 in your store a week before, but it doesn't work today.
我上周在你们店里买了个MP4，可是今天却不能用了。

Have you brought your receipt?
您带来收据了吗？
Yes. Here you are.
带了，给你。
I'm sorry. We will change yours for a new one.
抱歉，我们会给你换一个新的。