句型11
It强调句型
强调句的基本构成：It is/was + 被强调的部分 + who(主要指人时)/that + 其余部分
[注意1]
这种结构可以强调句子的主语、宾语、状语(包括时间，地点，方式，原因等)，但是不能强调谓语动词(参考句型15)。
原句的谓语动词如果是现在或将来时态，用It is…that/who….;
原句的谓语动词如果是过去时态，用It was…that/who….;
强调时间、地点、原因或方式时不要用when, where或how, 必须用that。
[例句1]
I saw him in the street yesterday afternoon.
→It was I who saw him in the street yesterday afternoon.(强调主语)
→It was in the street that I saw him yesterday afternoon.(强调地点状语)
→It was yesterday afternoon that I saw him in the street.(强调时间状语)
→It was him that/who I saw in the street yesterday afternoon.(强调宾语)
[例句2]
He didn't go to bed until his mother came back.
→It was not until his mother came back that he went to bed.
He didn't do his homework until his father came back from work.
→It wasn't until his father came back from work that he did his homework.
[例句3]
Only when you nearly lose someone do you fully realize how much you value him.
→It is only when you nearly lose someone that you fully realize how much you value him.
只有你快要失去某个人时，你才意识到你是多么尊重他。
[例句4]
I was late again because the traffic was very heavy during the rush hour.
→It was because the traffic was very heavy during the rush hour that I was late again.
(强调句中只能强调由because引导的原因状语从句，because不能换成since, as, for, now that等)
[注意2]
强调句的疑问结构
一般疑问句 Is / Was it +被强调部分 +who / that …?
特殊疑问句 特殊疑问词+is /was +it +who / that…?
What is/was it that…? Who is/was it that…? When is/was it that…?
Where is/was it that…? Why is/was it that…? How is/was it that…?
[例句1]
I saw him in the street yesterday afternoon.
→When was it that you saw him in the street?
→Who was it that you saw in the street yesterday afternoon?
→Where was it that you saw him yesterday afternoon?
[例句2]
I don't know when he will come back.
→I don't know when it is that he will come back.(宾语从句疑问词后用陈述句语序)
—How was it that you got in touch with Mr. Smith? 你是怎么和Smith先生联系上的?
—Trough a friend of mine. 通过一个朋友。

句型12
(1)祈使句(表条件)+ or/or else/ otherwise + 主句(表结果)… "否则…，要不然…"
(2)祈使句(表条件)+ and +主句(表结果)
[例句]
Hurry up, or you'll be late for class.
Please call me up before you come, otherwise/or else/or we might be out.
你来之前打个电话，否则，我们也许会出去。
Think it over and you will find the answer.
Give him an inch and he will take a mile. 得寸进尺。
Work hard and you will make progress every day. 好好学习，天天向上。

句型13
…until…"直到……时候";not…until…"直到……才……"
[例句]
You are to stay until/till your mother comes back. 你得等到你妈妈回来。
The meeting was put off until ten o'clock. 会议推迟到十点钟。
The villagers didn't realize how serious the pollution was until all the fish died in the river.
→Not until all the fish died in the river did the villagers realize how serious the pollution was.(倒装句)
等到湖里的鱼全死光了，村民们才意识到污染是多么严重。
He didn't go to bed until his mother came back.
→It was not until his mother came back that he went to bed.(强调句)
Not until he failed in the exam did he realize that he had wasted much time playing computer games.
Not until his son came back from school did he go to bed.

句型14
unless…"除非，如果不……"(=if…not)
[例句]
I shall go tomorrow unless it rains. 如果不下雨，我明天去。
—Shall Tom go and play football?
—Not unless he has finished his homework. 除非他完成作业，否则不能出去。
I won't go unless he comes to invite me himself.
除非他本人来邀请我，不然我是不会去的。
I won't attend his birthday party unless invited (=unless I am invited). 除非被邀请，否则我不去参加的生日晚会。

句型15
when引导的从句
when除了用来引导主语从句、宾语从句、时间状语从句、表语从句和定语从句，还有一种用法值得关注，那就是when引导并列分句，意思是"这时突然;就在那时"，强调另一个动作的突然发生。常用于以下句型中：(1)主语 + be doing… when…意思是"正在做某事这时……";(2)主语 + be about to do…when…;(3)主语+be on the point of (doing) …when…意思是"正要去做某事这时……"
[例句]
One day Chuck was on a flight across the Pacific Ocean when suddenly his plane crashed. 有一天，Chuck正在太平洋上飞行，这时他的飞机突然爆炸了。
I don't know when he will arrive. 我不晓得他什么时候到达。
I thought of the happy days when I was in Beijing. 我想起了在北京时的那段快乐日子。
I believe the time will soon come when there will be no weapons in the world. 我相信世界上没有武器的日子不久就会到来。
I was walking along the river when I heard a drowning boy cry for help. 我正在河边行走，这时我突然听到一个落水男孩求救。
I was about to leave when it began to rain. 我刚要离开，这时下雨了。
I had just finished my exam paper when the bell rang, announcing the class was over. 我刚做完作业，下课铃响了。
I thought of the happy days when I was in France. 我想到了在法国时那段快乐日子。
[比较]
I was walking along the street when I caught sight of a tailor's shop. 我正在街上走，这时我看见一家裁缝店。
I was walking along the streets. Just at the moment I caught sight of a tailor's shop. 我在街上走。就在那时我看见一家裁缝店。