如题所述
肯定句变否定句20个例子英语如下：
1、I think she is there.
否：I don't think she is there.
2、He can sing this song and that one.
否：He cannot sing this song or that one.
3、Tom went to school too.
否：Tom didn't go to school either.
4、He has had supper already.
否：He hasn't had supper yet.
5、He had a good rest just now.
否：He didn't have a good rest just now.
6、Let's do it.
否：Don't let's do it.或Let's not do it.
7、He always gets there on time.
否：He never gets there on time.
肯定句变否定句方法：
1、be动词的否定式。
be 动词根据不同的人称和时态有不同的形式，在一般现在时中是am , is , are可用作联系动词，构成否定式时，一律在其后面加否定词not.
He is reading.——He is not reading. They are from China. ——They are not from China.
2、情态动词的否定式。
情态动词的否定式是在其后面直接加not. 如：
I can swim. ——I can't swim. He can dance. —— He can't dance. You should go to school at seven. ——You shouldn't go to school at seven.
3、实义动词的否定句。
实义动词变否定句时，要借助助动词do , does，在一般现在时中用do或者does其句子结构为：主语+ don't / doesn't+动词原形+其它 。
