否定形式：主语+didn'；t +谓语动词原形+其他。
1、was/were+not。
2、在行为动词前加didn'；t，同时还原行为动词。
例句：I didn'；t know you like coffee.——我不知道你喜欢咖啡。
肯定句变为否定句：
1、当句中含有情态动词或助动词could，would，should等时，可直接在其后面加not构成否定句。
例如：I could get you a concert ticket. → I could not / couldn'；t get you a concert ticket.
2、当句中含有系动词was，were 时，可直接在其后加not构成否定句。
例如：I was on the Internet when you called me. → I was not / wasn'；t on the Internet when you called me.
3、当句中谓语是除情态动词、助动词、系动词was，were以外的动词时，在该动词之前加did not / didn'；t，动词还原，构成否定句。
