(后跟动词原形，构成不定式，可用作主语、宾语、表语、复合宾语、状语等，还可以单独使用)(used before a verb to indicate the infinitive;the infinitive can be used as a subject，an object，a predicative，a compound object，an adverbial，etc;it also can be used alone when the infinitive is understood)：T～make mistakes is natural. 犯错误是很自然的(事情)。It's important for us～learn English. 对我们来说，学英语是非常重要的。want～finish the work on time 想按时完成工作;want～invest 打算投资;know what/how～do知道做什么/怎么做;used～do sth过去常常做某事;They are～be married soon. 他们很快就要结婚了。ask sb～come 邀请某人前来;persuade sb not～do sth 劝某人不做某事;leave early～catch the train 早点动身去赶火车;She opened her eyes～find her sister standing beside her. 她睁开眼睛发现她的姐姐站在身旁。T～tell you the truth，I don't know what the answer is. 实话告诉你，我不知道答案。I asked him～go with us but he refused～. 我让他和我们一起去，但他拒绝了。