题目内容：

there is和it is用法的区别

优质解答

there is表示“有”的意思,例如：
There is apple on the desk.这儿有一个苹果在桌上.
I.It is + adj.+ to do something结构
　　句中it是形式主语,真正主语是动词不定式to do something.因此也可以表达为to do something + is +adj..
　　e.g.It is amazing to drive past fields which seem to go on forever or whole hills covered with neat rows of grapevines.
　　本句形式主语为it.真正主语to drive…grapevines移到了句子后部,使句子变得平稳,不致主语太长.如果把真正主语放在前面,那么整个句子就显得头重脚轻.因此,就用it作为先行主语.
　　这种结构还有两种动词不定复合结构.
　　1.It is + adj.+ for somebody to do something
　　e.g.It was very difficult for them to fly because men have not got wings.
　　此句真正的主语是动词不定复合结构for them to fly.其中them是to fly的逻辑主语.
　　2.It is + adj.+ of somebody to do something
　　e.g.It is sensible_____ you to bring an umbrella in such weather.
　　A.in B.for
　　C.with D.of
　　答案为D.这里sensible跟逻辑主语you的关系是表达人的特点、性格、本质等.像此类形容词还有kind,foolish,clever,wise,friendly等.
II.It is +名词+ to do something结构
　　e.g.It is great fun to see the pandas walking in the zoo.
III.另外,it作先行主语时还有其他用法
　　1.it +及物动词+宾语+不定式
　　e.g.It cost me 100 dollars to repair the car.
　　It takes me two hours to finish my homework every day.
　　It gave me great pleasure to watch them.
　　2.it + be +名词/形容词+ doing
　　e.g.It is no use studying for an exam at the last minute .
　　It is a waste of time talking to him.
　　It is pleasant sitting here