It is hard for him to get rid of his bad habits.他很难改掉自己的坏习惯。 比较：
It is good lf you to help me with my English. 你真好，帮助我学英语。（强调you的特征＝You are good to help me.）
It is good for you to give up smoking. 戒烟对你有好处。（强调的是give up smoking这一行为＝of you to give up smoking is good.） F．分裂不定式
动词不定式to do通常是不拆开的，但偶尔也可在不定式符号to和动词原形之间插入一个副词，构成分裂不定式。
He was too ill to completely carry out that program.他病得太重，不能完成那个项目。 He has made up his mind to once more try this method. 他已经下定决心再试试这个方法。 G．用作独立成分的不定式
有一些不定式短语可以作状语修饰整个句子，也可被称为插入语。
To be honest, we are not sure to find the girl in the forest.说老实话，我们不能确保在森林里能找到那个女孩。
To be frank, I don't agree with what you said. 坦率地说，我不同意你说的话。 必背：用作独立成分的不定式 to tell you the truth说老实话 to be frank 坦率地说 to begin with首先 to be brief简言之
to make a long story short长话短说 to be exact精确地说 to say nothing of姑且不说 to conclude总而言之 to be sure诚然，固然
to do him justice说句对他公道的话 so to speak可以这么说
H．用主动式表示被动含义的不定式
动词不定式在句中究竟用主动还是被动，有时比较复杂，主要有下面几种情况： 1．不定式做后置定语，和被修饰的名词或代词构成逻辑上的动宾关系，但又和该句主语构成逻辑上的主谓关系时。
Do you have anything to say on this question针对这个问题你有什么要说的吗？ He is a pleasant person to work with.他是一个与其合作起来令人感到愉快的人。
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2．不定式作形容词的宾语，和句子主语构成逻辑上的动宾关系时。 The book is difficult to understand.这本书很难理解。 The chair is comfortable to sit on.这把椅子坐起来很舒服。 3．There be结构中，当说话人考虑必须有人去完成某件事时。 There is nothing to worry about.没什么可担心的。 There is nothing to fear.没有什么可害怕的。 比较：
There is a lot of work to do.有许多事情要做。（表示某人必须做这工作） There is a lot of work to be done.有许多事情要做。（强调有许多事情必须做） She has two letters to type.她有两封信要打。（自己打） She has two letters to be typed.她有两封信要打。（别人打） I．表示虚拟语气的不定式完成式。
I hoped to have met him at the railway station, but he didn't turn up.我本希望在火车站接到他，但他未露面。
We would love to have gone to the match, but the tickets were all sold out.我们原想去看这场比赛的，但票已售完了。
The plane was to have taken off at 9, but something went wrong.飞机原计划九点起飞，但出现了一些故障。 J．用于感叹句。
不定式可用于感叹句，含有惊异、不满、惋惜或赞美等感情色彩。 To think that he should do this!想想，他竟然干出这等事！（表示惊讶） Oh, God, to see her dance !哦，天哪，看看她的舞蹈！（表示赞美）
To think that all the money has been wasted.想想，所有的钱都被浪费掉了！（表示不满）二、关于不定式符号的几个问题 A．不带to的不定式
1．在口语中，动词原形come和go后可接不带to的不定式。 Go tell her.去告诉她吧。 Come have a glass.来喝一杯。
2．在why引起的一些问句中，疑问词直接跟动词原形或not+动词原形。 Why make so much noise 为什么发出这么大的噪音？ Why not join us 为什么不加入我们？
3．在had better, had best, would rather, would rather...than, would sooner, would sooner...than, cannot but, cannot choose but, cannot help but等结构后直接跟动词原形或not +动词原形。 You'd better listen to your teacher's opinion. 你最好听一听老师的意见。
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