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1、概念引入上个单元中，我们已经学习it作代词和形式主语、形式宾语的用法，现在将继续学习it引出强调句的用法及一些与it有关的重点句型。先看这些句子：1. There is no doubt that the earth is becoming warmer and that it is human activity that has caused this global warming rather than a random but natural phenomenon.2. It was a scientist called Charles Keeling, who made accurat
2、e measurement of the amount of carbon dioxide in the atmosphere from 1956 to 1997.3. They also agree that itis the burning of more and more fossil fuels that has resulted in this increase in carbon dioxide.4. It was during the 20th century that the temperature of the earth went up about one degree F
3、ahrenheit.这些句子都是强调句，中的斜体词部分标识出了句中的强调句结构。用法讲解it引出的强调句1强调句的结构：It is / was + 被强调部分（主语，宾语，状语）+ that (who / whom) + 其它部分在强调句型中：1. 被强调部分可以是主语、宾语或状语。2. 引导词一般用that，如果是人的话，强调主语还可以用who，强调宾语用who和whom皆可。3. 判断一个句子是否是强调句，我们可以把被强调部分放回到句子中不需要添加任何成分时，句子就是强调句需要注意的是，在考试中，有的题会迷惑大家，许多题以It is开头，但是It is开头的句子并不全是强调句。那么如何判断
4、呢？看下列例句：1. It was in 2003 that I graduated from the university. 是在2003年我们从大学毕业的。 此句中有强调句结构“It was. that”，是不是强调句呢？把in 2003放回到原来句子中，即： I graduated from the university in 2003. 此句非常完整，不缺少成分，是强调句。2. It was not until dark that he realized it was too late to return home. 直到天黑他才意识到太晚了，不能回家了。 把强调句结构“it was.
5、 that”去掉，句子变成： He realized it was too late to return home not until dark.（非正常句子） 这是强调句中一个特殊的用法，它的原句应该是： He didnt realize it was too late to return home until dark. 注意：not. until句型中，如果写成强调句的话，要把not和until.部分一起提前。3. Was it in the village which we used to live in that the accident happened? 是在我们过去住的那个村子
6、发生的事故吗？ 此句是疑问句，较复杂的句子如果不好分析时，可以把原来的疑问句改成陈述句，变化得出： It was in the village which we used to live in that the accident happened. 去掉It was，句子中that前是从句“which we used to live in”修饰village，译成“我们过去住过的村 子”，是定语从句，which代替village作live in的宾语。原句应该是： The accident happened in the village which we used to live in. 考试
7、时经常把此条件句中which和that处变成空白处，看看你是否知道填什么词汇。那么分清何处是定语 从句，何处是强调句，就很关键了。 注意：强调句的一般疑问句形式，把it is/was中的is/was提前。4. Where was it that the road accident happened yesterday? 昨天是在哪儿发生的交通事故？ 此句也是疑问句，变成陈述句： It was where that the road accident happened yesterday. （非正常句子） 这个强调句的被强调部分，是疑问词，原句是： Where did the road acci
8、dent happen yesterday? 注意：强调句中如果提问被强调部分，要把疑问词放在句首，后面接一般疑问句语序。5. It is how you behave in difficulties that shows what you are really like. 是你在困境中的行为表现出你到底是什么人的。 去掉“It is. that”，句子变成： How you behave in difficulties shows what you are really like. 是强调句，因为句子很完整，强调的是主语从句。it引出的强调句2强调句型的几点注意：1. 句首词用“It”，不能
9、用“This”，“That”等。2. be动词总用单数形式，即is或was。可以用might be/ must have been/ cant be等形式。 It might be tomorrow evening that the news will be broadcast. 这则消息或许是明天晚上播出。3. 被强调的部分如果是表示“人”的代词，强调主语用主格，强调宾语用宾格。 It is him that (who/ whom) I met in the street yesterday. 我昨天在街上遇到的是他。 It is I that/ who didnt realize all
10、my mistakes until you told me yesterday. 是我直到昨天你告诉我才意识到我的错误。4. 连接词一般用that，当强调部分是人时，强调主语也可用who，强调宾语也可用whom或who。 当强调部分是时间状语或地点状语时，不能用when或where。 It was about 30 years ago that we graduated from university and became teachers. 我们是30年前从大学毕业成为老师的。 It was on Oct. 1st, 1949 that Peoples Republic of China w
11、as founded. 中华人民共和国是1949年10月1日成立的。 It is in the university where he taught that the research is carrying on. 这项研究是在他教过书的大学里进行的。5. 强调句中的主谓一致问题 若强调部分是句子的主语，则that或who引导的句子中的谓语动词应和强调部分保持人称和数的一致， 即：若被强调部分是单数，谓语动词用单数形式；若被强调部分是复数，则谓语动词用复数形式。如： It is Mary who often helps me with my English. 是玛丽帮我学英语的。 It is
12、 the boy students of Class Two who are playing football on the playground. 是二班的学生正在操场上踢足球。易与强调句混淆的几个句型1. It is/has been +时间+since . 从.以来有. since引导的从句通常是一般过去时，如果It is改成It was，since从句常用过去完成时。 It is years since I enjoyed such a good dinner. 我多年没有享受过这么好的一顿晚饭了。 It was five years since his father had died
13、. 当时他父亲去世五年了。2. It is +时间+ when . 当的时候，时间是 when 引导的是时间状语从句，主句中的 it 指时间，表语由具体的时间充当。 It was 10 oclock when we got home last night. 我们昨晚到家时十点了。 对比： It was at ten oclock that we got home last night我们昨晚是在十点到家的。 此句是强调句，去掉“it was.that”后句子仍然完整合理，注意that不能改成when。而上句不是强调句3. It was/ will be . before . 过.就. It w
14、as not/ will not be. before. 不久.就. 主句中的 it 指时间，表语多是long, not long , three days , two weeks 等表示“一段时间”的词或短语。 It was three days before he went to Beijing. 三天后他就去了北京。 It will not be long before he finishes his job. 不久他就完成了工作。 对比： It was three days ago that he went to Beijing. 他是三天前去的北京。 此句是强调句，去掉“it was.that”后句子仍然完整合理。it的常用句型小结11. It is clear (obvious/ true/ possible/ certain) that 某事是清楚（明显/真的/可能/肯定）的 It was clear that they had no desire for peace. 很清楚他们没有和平的愿望。2. It is important ( necessary, right, strange, natural.) that . 与上述句型属同一句型，但由于形容词不同，此句型that 后的从句中多用虚拟语气 （shoul
