while walking the dog=while you were walking the dog。本句中while后面省略了主语you和be动词were。由此可见,when或while引导的时间状语从句, 如果从句中的主语和主句的主语一致时,且谓语含有be动词,可省略从句中的主语和be动词。

　　【尝试运用】

　　While 　　　 in the countryside,he made many friends with the native there.

　　A.worked B.working

　　C.he works D.he is working

　　2.I wonder if it's because I haven't been able to be outdoors for so long that I've grown so crazy about everything to do with nature.我不知道这是不是因为我长久无法出门的缘故,我变得对一切与大自然有关的事物都无比狂热。

　　【观察思考】

　　1)It was yesterday that I met Ann in the street.我是昨天在街上遇见安的。

　　2)It is he who is going to speak at the school meeting.是他要在校会上发言。

　　3)It was in the street that I met my old friend yesterday.昨天我是在街上碰到了我的老朋友。

　　4)Was it you that/who let out the secret to her? 是你把这个秘密泄露给她的吗?

本句含有It is/was+被强调部分+that/who+其他成分的强调句型。强调句型可对句中的主语、宾语、表语、状语等进行强调,若强调的是人,后面的that也可用who代替。

如:I met Li Ming at the railway station yesterday.昨天我在火车站遇到了李明。

1)It was I that/who met Li Ming at the railway station yesterday.(强调主语)

2)It was Li Ming that/ whom I met at the railway station yesterday.(强调宾语)

3)It was yesterday that I met Li Ming at the railway station.(强调状语)

　　【尝试运用】

　　1)I don't mind her criticizing me,but 　　　 is how she does it that I am against.

　　A.it　　　　　　　　B.that　　　　　　　C.this　　　　　　　D.which

　　2)It is not who is right but what is right 　　　 is of importance.

　　A.which B.it C.that D.this

　　3....it was the first time in a year and a half that I'd seen the night face to face...

　　......这是我一年半以来第一次目睹夜晚......

　　【观察思考】

　　1)It is the first time that the boy has gone home alone.这是那个男孩第一次单独回家。

　　 2)This was the fourth time she had rung you in a week.这是她一周内第四次给你打电话。

　　 3)That will be the tenth time that I have visited Beijing.那将是我第十次参观北京。

It / This / That is the first (second,third...)time that 主语.have/has/had done sth.是一常用句型,意为"某人第一(二、三......)次做某事"。从句中的时态须用完成时态。

　　【尝试运用】

　　1)It's the first time that he 　　　 (write)a letter in English.

　　2)-Do you know our town at all?

　　-No,this is the first time I 　　　here.

　　A.was B.am coming

　　C.came D.have been

4.Another time five months ago,I happened to be upstairs at dusk when the window was open.还有一次,就在五个月以前的一个黄昏,我碰巧在楼上,窗户是开着的。