动词ing形式的双写是有规则的，也就是当最后一个字母前前面是元音字母时，才需要双写y，在这里buy中的字母u不发音。
例句：
We're buying a new TV with the money.
我们要用这笔钱买一台新电视机。
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。
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