*Ⅳ不定式的完成式和进行式的用法 (仅仅需要稍微了解即可)
1.完成式表示的动作发生在句子谓语表示的动作之前。如：
I’m sorry not to have come on Thursday. 来源：
星期四那天我没有来，很抱歉。
The earth is said to have been part of the sun.
据说地球过去曾经是太阳的一部分。
2.进行式一般表示正在进行中的动作，强调与谓语动词所表示的动作几乎同时发生。如：
I noticed that he seemed to be smoking a lot.
我注意到他似乎烟抽得太多。
I happened to be lying in bed when she came in.
她进来时，我碰巧正躺在床上。
小结：
1) 不定式可做除谓语以外的任何其他成分----主语、宾语、宾语补足语、表语、状语、定语：不定式本身也有时态和语态的问题。每个不定式都有其逻辑主语，如果逻辑主语是动作的发出者，不定式用主动式，如果其逻辑主语是动作的承受者，不定式用被动式。
如：The doctor recommended him to clean the room. 医生建议他打扫房间。
如：The doctor recommended the room to be cleaned. 医生建议打扫房间。
2) 不定式的符号to 在一些特殊情况下经常被省略。
A) 当几个动词不定式具有同样的功能时，to 只用在第一个动词不定式之前。
B) 在以why 引导的疑问句中不用to
e.g. He asked why (to) stay here.
C) 在had better, would rather, rather than, would sooner(宁愿), can not but(不得不), cannot help but, do nothing but(只能)等结构后不用to
D) 在hear, listen to, feel, see, look at, watch, notice, let, make, have, leave, help等动词后，动词不定式做宾语补足语时不用to
不定式结构的考察在职称英语考题中主要是以完成句子题(可能涉及到不定式结构)和文章中句子句意理解这样的题出现。
如：2003年综合B/A级完成句子考题：Keeping Cut Flowers
30. Another important way to prolong the life of cut flowers is ____.
A. by keeping its original shape and color
B. in the life of the cut flower
C. to produce carbon dioxide
D. for as long as possible
E. by controlling temperature
F. to replace the water and solution every day
文章相关句子：Another vital factor in keeping cut flowers is the quality of the water…
……………. The water and solution should also be replaced each day.
如：2002年理工类阅读理解第1篇文章Mobile Phones中的第一个问题：
According to Robert Bell, if mobile phones prove to be dangerous to people's health,(系动词+ 表语)
A. they should be banned immediately.
B. the use of them should be restricted.
C. all transmitter to towers should be torn down.
D. a warning label should be attached.
解答：问题问“如果手机被证明对人的健康有害，那么。。”，文章中第1段的最后一句：If mobile phones are found to be dangerous, they should carry a warning label until proper shields can be devised. 该句的不定式结构表述的语义与问题句中条件句(带不定式结构的谓语)的含义一致，所以判断该句是答案相关句，并根据句意选择答案D。
2005年卫生类C级阅读理解文章中也有考题直接涉及到不定式结构:
If you draw your money before it is due, you will have to ___.
A. pay interest to the bank

        B. open a new account
C. pay a penalty or fee
D. 分析: have to 是“不得不/必须”， to是不定式符号。问题句是说“如果在你在你的前的前到期之前取钱，你将不得不…”。借助我们的相关背景知识可以对这道题进行直接判断：D(支付违约罚金或手续费)合适。