一、肯定句改为否定句
1. 改变谓语结构
在系动词be, become, feel, smell等，助动词 be, have, do 等以及情态动词can, may, should等后加not。如果句子的谓语中不是以上这些词，而是行为动词，则相应地将动词的原形 ，第三人称单数或过去式 变为否定形式。如：
He has seen the film before.
→He hasn’t seen the film before.
He will write the book in two months.
→He won’t write the book in two months.
He does his homework in the evening.
→He doesn’t do his homework in the evening.
