肯定句变否定句20个例子英语如下：
1、肯定句：She is going to China next month.
否定句：She isn't going to China next month.
2、肯定句：There were some ducks and chickens on the farm too.
否定句：There weren't any ducks or chickens on the farm either.
3、肯定句：I am a teacher.
否定句：I am not a teacher.
4、肯定句：I can play the pianno well.
否定句：I cannot play the pianno well.
5、肯定句：His family will fly to Beijing.
否定句：His family won't fly to Beijing.
6、肯定句：The little boy should go to bed early.
否定句：The little boy shouldn't go to bed early.
7、肯定句：The students often sing songs after school.
否定句：The students don't often sing songs after school.
8、肯定句：The boys runs fast.
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