I have ashortruler.怎么改变否定句？
I have a short ruler.改为否定句是：I have not a short ruler.
【怎样改为英语否定句】
如果句子中有be动词、情态动词和助动词时可以再be动词、情态动词和助动词后加not
例如：I am a teacher.→I am not a teacher.
She can help me.→She can't help me.
Yes,I do.→No,I don't.
如果句中谓语动词为行为动词时，要根据时态选用do的相应形式，把肯定句变为否定句。
例如：The little girl wants to go there.
→The little girl doesn't want to go there.
He did his work yesterday.→He didn't do his work yesterday.
如果是祈使句变否定句时，一般在句首加Don't，但Let us或Let's开头的祈使句在 Let us或 Let's后加not即可。
例如：Put them over there.→Don't put them over there.
Let us go home.→Let us not go home.
如果主从复合句中，主句是I think，I believe等结构，变否定句时，形式上否定主句，实际上否定从句。
例如：I think chickens can swim .我认为鸡会游泳。
→I don't think chickens can swim .我认为鸡不会游泳。
如果剧中有“had better +动词原形”，变否定句时为“had better not +动词原形”。
例如：You'd better go to school.→ You'd better not go to school.
动词不定式变否定式时，常在不定式to前加not。
例如：The teacher tells me to do it.→The teacher tells me not to do it.
如果句中有使役动词和感官动词(make，let，hear，see，watch等)后接省略to的不定式，此种不定式变否定句时只需在省略to的动词原形前加not。
例如：I saw her work.→I saw her not work.
