PART 1
The functions of To-infinitive
动词不定式由“to+动词原形”构成，其否定形式是not to do。动词不定式可以单独使用或用作动词不定式短语的一个部分。不定式在句中可做主语、宾语、状语、表语、宾语补足语和定语等，但不能单独作谓语.
1.
动词不定式做主语时，为了句子平衡，通常用it做形式主语，而把不定式放在谓语之后。例如：To read English every day is necessary.
=It is necessary to read English every day.
To go for a picnic today is a good idea.
=It is a good idea to go for a picnic today.
2不定式做宾语时，若还带有宾语补足语，往往把不定式放在补足语后，用it做形式宾语。例如：He find it difficult to learn Chinese.
We think it important to master a foreign language.
3.
He invited me to give a speech on Chinese histor
（不定式to give a speech on Chinese history 做宾语补足语，补充说明宾语me） He asked me to help him with his English.
The General ordered the soldiers to fight till the last minute.
I wanted to go.
1)I have a letter to post.
(不定式to post做定语，修饰名词letter)
做定语的不定式如果是不及物动词，不定式后面须有相应的介词。
例如：She had only a small room to live in.她有个小房间可以住在里面。
I need a pen to write with.我需要一支笔去写。
2) 试比较：
Do you have anything to wash? 你有什么要洗吗？
(不定式to wash的动作执行者是you)
Do you have anything to be washed? 你有什么要（别人）洗吗？
（不定式to wash的动作执行者是别人，而不是you）
5.
His wish is to become a lawyer.
(不定式to become a lawyer在连系动词is后做表语)
His job is to raise pigs.他的工作就是养猪。
To see is to believe.百闻不如一见。
They worked hard day and night to pay back the debt.表目的
I hurried to the airport only to find the plane had taken off.表结果
She felt disappointed to hear the news that she hadn’t been promoted.表原因
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