比较过去时与现在完成时举例： I saw this film yesterday. （强调看的动作发生过了。） I have seen this film. （强调对现在的影响，电影的内容已经知道了。） 用于现在完成时的句型1）It is the first / second time…. that…结构中的从句部分，用现在完成时。 It is the first time that I have visited the city. It was the third time that the boy had been late.2）This is the… that…结构，that 从句要用现在完成时. This is the best film that I've (ever) seen. 这是我看过的最好的电影。比较since和forSince 用来说明动作起始时间，for用来说明动作延续时间长度。since的四种用法1) since +过去一个时间点 (如具体的年、月、日期、钟点、1980, last month, half past six)。 I have been here since 1989. 2) since +一段时间+ ago I have been here since five months ago. 3) since +从句 Great changes have taken place since you left. Considerable time has elapsed since we have been here. 4) It is +一段时间+ since从句 It is two years since I became a postgraduate student.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。过去完成时表示过去的过去----|-------|-----|---->其构成是had +过去分词构成。那时以前 那时 现在 过去完成时的时间状语before, by, until , when, after, once, as soon as。现在进行时现在进行时的基本用法： a. 表示现在( 指说话人说话时) 正在发生的事情。 We are waiting for you. b. 习惯进行：表示长期的或重复性的动作，说话时动作未必正在进行。 Mr. Green is writing another novel. (说话时并未在写，只处于写作的状态。) c. 表示渐变的动词有：g...
