表示原因时，分词短语常放在句首，也可放在句未，多用逗号隔开；不定式短语却只能放在句末，但不用逗号，且多用于表示情绪或情感反应的动词、形容词(如happy, glad, sorry, sad, surprised, frightened, delighted, disappointed)之后。如：
1. I’m surprised to see you here. 在这时遇到你真让我感到意外。
2. ________ by the beauty of nature, the girl from London decided to stay another two days off the farm. (辽宁卷)
A. Attracting B. Attracted
C. To be attracted D. Having attracted
【分析】答案选B。在句首表示原因不能用不定式，排除C；句子主语the girl与attract是被动关系，用过去分词短语作原因状语。
3. ________ in thought, he almost ran into the car in front of him. (全国卷)
A. Losing B. Having lost
C. Lost D. To lost
【分析】答案选C。表示原因不能用不定式，排除D；句子主语he与lose是逻辑上是被动关系，用过去分词: Lost in thought…=As he was lost in thought… 此处的过去分词实际上是表示状态的形容词，用汉语思维难于理解，除be lost in thought(沉思)外，这类惯用结构还有be caught in the rain(遇到雨), be dressed in red(穿着红衣), be seated in a chair(坐在椅子上)等，并注意这类结构作补语或后置定语时也要用过去分词。
4. ________ his telephone number, she had some difficulty getting in touch with Bill. (上海卷)
A. Not knowing B. Knowing not
C. Not having known D. Having not known
【分析】答案选A。现在分词的否定式在前面加not，“不知道电话号码”与“难与Bill联系”同时发生的不用完成式。Not knowing…=As she didn’t know…
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