could的否定形式是couldnt或could not.
couldmodal用于can的过去时；(询问是否可做某事)能，可以；(礼貌地请求别人做事)能
I couldn\'t get the car to start this morning.
我今天早上没法让这汽车发动起来。
I couldn\'t understand a single word she said!
她讲的东西我一个字都听不懂！
We couldn\'t understand them because they were talking in Chinese.
我们听不懂他们在讲些什么，因为他们说的是汉语。
