英语,句子怎么变否定句?如题.最好带上例子

先看句子里有没有be动词（am,is,are）、情态动词(can,may,would),如果有,在这些词后面直接加not
如果没有,就在谓语动词前加don't,doesn't 或者didn't
例如：
He is a student.He isn't a student.
She can fly a kite.She can't fly a kite.
I go to school by bus.I don't go to school by bus.
He likes to play football.He doesn't like to play football.

1. 主系表结构的句子，只需在系动词加not。如：He is wasa teacher --- He isn't wasn`t a teacher .
2. 主谓宾结构的句子，根据时态和人称用助动词适当形式加 not 。如：
He she works hard ---He doesn't work hard .一般现在时态的第三人称单数，注意用 doesn't ...

举例说明
1. He is a teacher ---He isn't a teacher
2.I am a teacher ---I am not a teacher
3. You are tall ---You aren't tall
4 He works hard ---He doesn't work hard
5 I word hard --...

先看句子里有没有be动词（am,is,are）、情态动词(can,may,would)，如果有，在这些词后面直接加not
如果没有，就在谓语动词前加don't,doesn't 或者didn't
例如：
He is a student. He isn't a student.
She can fly a kite. She can't fly a kite.