也就是说，只要把握好"时间状语"和"语态(先行词与动词的关系)"，非谓语动词做定语的考试选项比较容易，出题几率也比较低。
有人可能会问：
I have a letter to write 和I have a letter to be written两个句子中的黑体部分都是做"letter"的定语，为什么一个用主动，另一个用被动语态。一般来说，当动词(write)的行为者就是句子的主语(I)时，用主动语态。因此，这两个句子的内涵是有些区别的。但由于考试形式的局限性，一般不会考这种区别的。
4.状语
非谓语动词做状语是这一讲的重点，也是考医.学.全.在.线www.med126.com试的重点。大家还记得"句子的连接"一讲中说过的"逗号不能连接两个句子"这句话和所举的例子吗?
错：He is ill, he cannot come to the party this evening.(逗号不能连接两个句子)
对：Because he is ill, he cannot come to the party this evening.(使用连接词)
对：Being ill, he cannot come to the party this evening.(使用非谓语动词形式)
如果：His child is ill, he cannot come to the party this evening. 该怎么改呢?
道理是一样的：
His child being ill, he cannot come to the party this evening.
也就是说，非谓语动词也要有"行为的主体"，称为"主格";如果"非谓语动词的行为的主体"与句子的主语不一致，要保留其行为主体(如上句中的"his child")，这种结构称为"(分词)独立主格结构".
下面每个例子说明一条规则，注意理解和记忆(重点不要去区分作什么状语，也不要刻意去翻译句子的意思，重点注意形式的转换和规律)：
1) When she heard the noise, she went out to see what was happening.
Hearing the noise, she went out to see what was happening.
规则：当句子的主语(she)与 (非谓语)动词构成主动语态时，只要将实义动词(heard)恢复原形 (hear)，后面加ing即可
2) When (或 If) the substance is heated to over 200℃, it will give off a poisonous gas.
Heated to 200 over 200℃, it (= the substance) will give off a poisonous gas.
规则：当句子的主语(it = the substance)与 (非谓语) 动词构成被动语态时，去掉be动词，只保留动词的-ed形式(heated)即可
3) As he did not want to hurt her feelings, he did not tell the truth at the moment.
Not wanting to hurt her feelings, he did not tell the truth at the moment
规则：非谓语动词的否定式是在非谓语动词前面(不是后面)加not构成;其他变化按照例1)或例2)规定
4) As she has lived in China for over 20 years, she can speak Chinese fluently.
Having lived in China for over 20 years, she can speak Chinese fluently.
As they had not finished the lesso医学全在.线www.med126.comns, the students had to give up going to see the play.
Not having finished the lessons, the students had to give up going to see the play.
规则：当句子中出现1)"for + 时间"状语，或2)当一个行为必须在另一个行为结束后才能开始的情况下，应该用"完成式"，否定词 "not" 要放在"having"的前面，即"Not having…"
提示：当你在考试时分不清是否要用"完成式"时，应倾向于选择有"完成式"的选项。
5) If weather permits, we'll go out for a picnic tomorrow.
Weather permitting, we'll go out for a picnic tomorrow.
When all necessary data had been collected, they began the experiment.
All necessary data having been collected, they began the experiment.
(注：这个句子也可以写成：All necessary data collected, they began the experiment.考试时按例4)提示选题)
规则：当句子的主语与非谓语动词的主格不一致时，应使用"独立主格形式"，其他变化按上述各项规定处理
需要说明的是：
1. 所谓"前置"和"后置"是相对的，这里这样区分一是为了便于理解，二是根据职称考试中出题的习惯，便于判题;
2. 关于功能，这里只是讲了考试中较多出现的形式和结构，对于诸如如何区分"目的"和"结果"等内容，因与解题关系不大，这里就不作具体说明了。
下面把非谓语动词中其他几个重要问题用实例说明一下：
关于"不定式"作后置状语的举例(注意黑体字部分的表达形式)：
1) She was so angry as to be unable to speak. (她气得连话都说不出来了。)
2) I don't know her well enough to ask her for help.(我与她不太熟悉，不便请她帮忙。)
3) She was too angry to say anything.(她气得什么都说不出来了。)
4) I'm only too glad to help you.
注意与例3)的区别：only too与happy, pleased, glad 等词使用时，表示"非常"：我非常愿意帮助你(能帮助你真是太高兴了)。
