don't, didn't, haven't, wasn't都是表示否定的结构。

don't对句中的行为动词进行否定，第三人称单数用doesn't。如，I don't know whose shoes are these.我不知道这些鞋是谁的。

didn't是don't的过去式形式，对行为动词过去式进行否定。如，He didn't come to school today.他今天没来上学。

haven't在两种情况下可以使用，第三人称单数用hasn't。一是表示“有”的时候，二是在完成时态中作助动词时。如，I haven't any brothers.我没有兄弟。He hasn't finished his home work.他还没有做完家庭作业。

wasn't是isn't和am not的过去式形式，复数是weren't。是连系动词或助动词的否定，不再需要其他的助动词。如，I wasn't at home this morning.今天早上我不在家。My computer wasn't mended by Uncle Wang.（was是助动词，用于被动语态）我的电脑没被王叔叔修理。