buy后面加什么格

I want to buy a present for my mother and father.

我想给爸爸妈妈买件礼物。

It would be more economical to buy the bigger size.

买尺寸大点的更实惠。

We make sure our clients get the best that money can buy.

我们确保客户买到最好的产品。

We need to buy some new furniture.

我们需要买一些新家具。

They've bought themselves a new car.

他们给自己买了一辆新车。