一般现在时怎样变否定句

一般现在时怎样变否定句

一般现在时变否定句的规则：
(a) 含有 am is are 的句子,变否定句时,只需在am is are 后加not.
例：This is a book.
否定句：This is not a book .

(b) 含有实义动词的句子,变否定句分两步.
（1）如果主语是第三人称单数时,要在实义动词前加doesn't,后面的动词用原形.
例:He eats an apple.
否定句:He doesn't eat an apple.

(2) 如果主语不是第三人称单数时,只需在实义动词前加don't.
例:I teach English.
否定句 I don't teach English.

(c) 含有情态动词的句子,变否定句时,只需在情态动词后加not.
例:I can dance.
否定句 I can not dance.
或 I can't dance.

析：当must be用来表示推测,有“一定”的含义时,否定式要用can not.
例:You must say something at the mecting.
You needn’t say anything at the mecting.

析：当“must+行为动词”用来表示“必须”的含义时,其否定式可用needn’t 或mustn't表示“不需要”,“不必”,语气委婉,must not表示“禁止”,“千万别”语气生硬.
例：You may come in now.
You mustn't come in now.

析：may作为情态动词表示“可以”时,其否定式用must not,而不用may not.
例： He may watch TV .
He mustn't watch TV.

注意:
(1) 见到some 变否定句时,要换成any.
例： I eat some apples.
否定句 I don't eat any apples.

(2) 见到and 变否定句时,要换成or.
例：There is some air and water on the moon.
否定句 There isn't any air or water on the moon.

(3) 见到too和also变否定句时,要换成either.
例:Tom goes to school too.
否定句 Tom doesn’t go to school either.
too和also用于肯定句中时,否定句中用either替换.
（4 )见到already变否定句时,要换成yet.
例:He has had supper already.
He hasn’t had supper yet.
随着对谓语动词的否定,某些副词也要作相应的变动.