肯定句如何变否定句？

　　一、借助否定词

　　在be动词(am/is/are/was/were)后加“not”

　　例如：“He is a student.” 变为否定句：“He is not a student.”

　　“They were happy.” 否定句：“They were not happy.”

　　在情态动词(can/could/must/should等)后加“not”

　　如：“You can do it.” 否定句：“You can not do it.” (通常缩写为“can't”)

　　“She must go.” 否定句：“She must not go.” (通常缩写为“mustn't”)

　　在实义动词前加“do/does/did + not”，且实义动词变回原形

　　“He likes music.” 否定句：“He does not like music.” (缩写为“doesn't”)

　　“I went to Beijing last year.” 否定句：“I did not go to Beijing last year.” (缩写为“didn't”)

　　二、使用否定形容词或副词

　　例如：“She is beautiful.” 否定句：“She is not ugly.” (用“ugly”这个否定意义的形容词)

　　三、借助“no”“never”“seldom”“hardly”“rarely”“few”“little”等词

　　“There are some books on the desk.” 否定句：“There are no books on the desk.”

　　“He often plays football.” 否定句：“He seldom plays football.”

　　四、注意事项

　　转换时要注意主谓一致，确保否定词的使用正确。

　　留意句子的时态，不同时态下否定词的形式也有所不同。

　　对于一些固定短语和句型，其否定形式也有特定的规则，需要特别记忆。

　　例如：“both...and...”的否定形式是“neither...nor...”;“too...to...”的否定形式是“not...enough to...”