上几期学习了英语语法：语态转换-主语+谓语动词+宾语+（疑问词）+不定式。本期学习英语语法：语态转换-主语+谓语动词+宾语+（疑问词）+不定式。
动词不定式是一种非谓语动词，其结构为“（to）+动词原形”。
（1）不定式用作主语
to不定式常常用作句子主语，但多数情况下常用it作形式主语，将to不定式后置。比如：
飞行对人类来说曾经很困难。
To fly was difficult for human beings.
It was difficult for human beings to fly.
参加运动和娱乐很重要。
To take part in sports and recreation is important.
It is important to take part in sports andrecreation.
外国人说中国话不容易。
To learn to speak Chinese is not easy for a foreigner.
It is not easy for a foreigner to learn to speak Chinese.
在某些形容词kind, good, nice,clever, careless, stupid等作表语时，不定式前常可加一个of引起的短语，说明不定式指的是谁的情况。比如：
It’s kind of you to say so.
你这样说太好了。
It’s careless of you to give me the wrong number.
你很粗心，给我错的电话号码。
It was stupid of him to buy such a thing.
他很笨，买这样的东西。
to不定式还可以用于结构“it + take + 一段时间+ to不定式”，解释为“花时间干某事”。比如：
It usually takes me half an hour to ride tomy office.
我通常花半小时驾车到我办公室。
It will take three days for the parcel to reach Beijing.
这个包裹寄到北京将要费时三天。
