cant释义：不可能，不能，是情态动词的否定式
The window can't open. 窗户设计的时候就不能打开，是固定死的。
doesnt是对一般现在时态第三人称行为动词的否定：
The window doesn't open. 窗户打不开。（纯粹陈述客观事实
can't是不可能的意思.
例：I can't move that box because it is so heavy.
don't是助动词.
例：I don't know.
did't是don't的过去式，在一般过去式的句子中改否定句是常用到.
例：He worked out this problem by himself.
否定句是：He didn't work out this problem by himself.
couldn't是can't的过去式.could也有时候表示委婉语气.
例：Could you give me that pen?
