Unit5RhythmPeriodThree　Grammar课件（北师大版必修2，广东专用）.ppt

Unit 5 Rhythm Period Three　Grammar 课件（北师大版必修2，广东专用）; ;I have written home four times since I came here. 自从我到这儿来，我往家写了四封信。 Once you remember it，youll never forget it. 你一旦记住了它，就永远不会忘记。 2．when除了作“当……时候”解之外，还有“那时(突然)，这时(突然)”之意，常用于下列句式：was/were doing...when...“正……突然……”；was/were about to/going to do...when...“正要……突然……”；had just done...when...“刚……突然就……”。 We were having a meeting when someone broke in. 我们正开会突然闯进一人。;We were about to set off on our way when it suddenly began to rain. 我们刚要出发，突然下雨了。 另外，when还可作“既然”解，引出原因状语从句。 It was foolish of you to take a taxi when you could easily walk there in five minutes. 既然能轻易地五分钟内步行到那儿，那么乘坐出租车你太傻了。;3．before“在……之前”，还可译为“还未……就……”；“不到……就……”；“……才……”；“趁着还没……就……”；“还没来得及……就……”等。 We had sailed four days and four nights before we saw land. 我们航行了四天四夜才看到陆地。 We hadnt run a mile before he felt tired. 我们跑了还不到一英里他就累了。 Please write it down before you forget it. 趁你现在没忘把它记下来。;Before I could get in a word，he had measured me. 我还没来得及插话他就给我量好了尺寸。 Before they reached the station，the train had gone. 他们还没到达火车站，火车就已开走了。;【辨析】 before/since before可构成句型：“it will(not)be...before”和“it was (not)．..before...”，意为“多久之后才……”。 It will be half a year before I come back. 还要半年我才回来。 It wont be long before we meet again. 过不了多久，我们又会见面。;It was some time before I realized the importance of it. 过了一段时间我才意识到它的重要性。 since可构成句型：“It is/has been...since...”，意为“做某事已有多久了；已有多久没做某事了。” It is three years since the war broke out. 战争爆发以来，有三年了。;It is three years since she was in our class. 她离开我们班有三年了。 It is three years since he lived here. 他不在这儿住有三年了。 It is three years since I smoked. 我不吸烟有三年了。 It is three years since I began to smoke.我吸烟有三年了。;4．while和as都可译为“在……期间；正当……时”，表示主句中的动作和从句中的动作同时发生。但while从句中的谓语动词通常是持续性动词，而as从句中的谓语动词既可是持续性动词，也可是短暂性动词。 Please dont talk so loud while others are working. 其他人工作时，请你们不要高声谈话。 While I was wondering at this，our schoolmaster took his place. 正当我对此不解时，我们校长就座了。 He hurried home，looking behind as he went. 他匆匆忙忙跑回去，一边走一边回头望。 John sings as he works.约翰一边工作，一边唱歌。;注意：as还可译为“随着”，