否定句:his+uncle+is+not+a+teacher。
如果句子的谓语本身含有be动词,直接在be后加not即可。例如:
She is goot at science.改为否定:She is not(isn't) good at science.
She is reading a book.改为否定:She isn't reading a book.
如果句子的谓语含有助动词have(用于完成时。注意是助动词,不是实意动词),直接在have后面加not即可。例如:
She has read this book.改为否定:She has not(hasn't) read this book.
She had finished the housework when I came back home.改为否定:She hadn't finished the housework when i came back home.
当句子含有情态动词时(can, could,must, should, shall, will, would, may,might等),直接在情态动词后加not。例如:
You can do it tomorrow.改为否定:You can't do it tomorrow.
但需注意,情态动词must表示必须做某事的时候,其否定不用mustn't(mustn't表示一定不能,而不是“不必”,而应该用needn't)。如:
Must i finish the task today?——No, you needn't.我必须今天完成任务吗?——不,不必今天。
如果陈述句是除了上述的情况以外的,也就是说句子的谓语不含有be、have、情态动词,而是其他实意动词时,改成否定就需要在动词前补充助动词do(需要根据时态和人称变换),然后再加not。
例如:
She likes reading books.改为否定:She does not like reading books.(此时还需注意,likes改为否定句时,应用动词原形)
She went shopping yesterday. 改为否定:She did (过去时)not go shopping yesterday.(went同样要改为原形)
They like reading books.改为否定:They do not (don't) like reading books.
总结:1,如果句中有be动词,在be动词后加not
2,如果句子中有谓语动词,在主语后加don't(如主语为第三人称则加doesn't,切变动词三单为原型)
3,如句子中有情态动词(如can,may等)在情态动词后加not即可
4,如句子由need to等句型构成,则在need这类单词后加not
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