新概念英语第三册 Lesson 20(课文5)

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Key structures
定语从句中介词位置
决定介词位置的4个因素:
1，在书面语中，当定语从句的关系代词是介词的宾语时，能够把可移位的介词提前放在关系代词的前面
e.g. This is the person about whom I was telling you.
e.g. Is this a book for which you asked me?
2，在口语中，介词一般要放在从句的末尾
3．有些“动词+ 介词”的合成词组被看成是不可分割的语言单位，这个时候介词必须紧跟动词，不可移动，如：take after  account for
4．在很多情况下，介词和关系代词构成独立的介词短语，在句中起状语作用，与从句的谓语动词毫无关系，而不是谓语动词的一部分，这时介词始终位于关系代词之前
e.g. He described it as a very agreeable situation located within two small hills in the midst of which flowed a great river.(in the midst of跟后面的谓语动词flow没有任何关系)
e.g. Mrs. Ramsay received an anonymous letter in which the writer stated that Rastus was in safe hands.