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公共英语pets二级语法基础知识
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延续动词与瞬间动词
1)用于完成时的区别
延续动词表示经验、经历; 瞬间动词表示行为的结 果，不能与表示段的时间状语连用。
He has completed the work. 他已完成了那项工作。 (表结果)
I've known him since then. 我从那时起就认识他了。(表经历)
2)用于till/until从句的差异
延续动词用于肯定句，表示"做……直到……" 瞬间动词用于否定句，表示"到……，才……"
He didn't come back until ten o'clock.
他到10 点才回来。
He slept until ten o'clock.
他一直睡到10点。
典型例题
1. You don't need to describe her. I ___ her several times.
A. had met B. have met C. met D. meet
答案B. 首先本题后句强调对现在的影响，我知道她的模样，你不用描述。再次，several times告知为反复发生的动作，因此用现在完成时。
2.——I'm sorry to keep you waiting.
——Oh, not at all. I ___ here only a few minutes.
A. have been B. had been C. was D. will be
答案A. 等待的动作由过去开始，持续到现在，应用现在完成时
过去完成时
1) 概念：
表示过去的过去
其构成是had +过去分词构成。
那时以前 那时 现在
2) 用法
a.在told, said, knew, heard, thought等动词后的宾语从句。
She said (that) she had never been to Paris.
b. 状语从句
在过去不同时间发生的两个动作中，发生在先，用过去完成时;发生在后，用一般过去时。
When the police arrived, the thieves had run away.
c. 表示意向的动词，如hope, wish, expect, think, intend, mean, suppose等，用过去完成时表示"原本…，未能…"
We had hoped that you would come, but you didn't.
3)过去完成时的时间状语：
before, by, until , when, after, once, as soon as.
He said that he had learned some English before.
By the time he was twelve, Edison had began to make a living by himself.
Tom was disappointed that most of the guests had left.
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