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句子中有When用什么时态?

when在中学英语教学中出现的频率较高,用法较多,现归纳如下:

一、用作副词

表示“什么时候”,常用作疑问副词、连接副词和关系副词等。

1.用作疑问副词,表示“何时,什么时候”,构成表示时间的特殊疑问句。例如:When will they come back?(他们什么时候回来?)

2.用作连接副词,意思是“什么时候”,引导名词性从句(主语从句、表语从句和宾语从句)。例如:Do you know when they are coming?(你知道他们什么时候来吗?)

3.用作关系副词,意思是“当……时候,在那时”,引导定语从句。例如:I will never forget the day when I joined the army.(我将永远忘不了我参军的那个日子。)/It happened ten years ago, when I was a child.(事情发生在十年前,那时我还是个孩子。)

二、用作从属连词

1.引导时间状语从句,意思是“当……的时候”。例如:It was raining when we arrived.(我们到达时天正下着雨。)

2.引导原因状语从句,意思是“既然”、“因为”,相当于since、when引导的从句往往放在主句之后。例如:How can they learn anything when they spend all their spare time playing computer games?(他们把所有的空闲时间都用来玩电游,还能学什么东西呢?)

3.引导让步状语从句,意思是“即使”、“尽管”、“虽然”,相当于even though、although。例如:They kept trying when they must have known it was hopeless.(他们明明知道那事没有希望了,但他们还继续在干。)

4.引导条件状语从句,意思是“如果”,相当于if。例如:Call me at once when anything goes wrong with the computer.(如果计算机发生故障,立即叫我。)

三、用作并列连词

when用作并列连词时的意思是“正在……,这时……突然”,连接两个并列句。例如:We were doing our homework when the light went out.(我们正在做家庭作业,就在那时灯熄灭了。)

四、用作关系代词

作关系代词的when可引导定语从句,意思是“那时”。例如:Mr. Smith came to China in 2002; since then he has been working in Beijing University.(史密斯先生于2002年来到中国,从那时起他一直在北京大学工作。)

五、用作疑问代词

表示“何时,什么时候”,例如:Until when can you stay?(你能呆到什么时候?)

六、用作名词

常与where、how等并列使用,指“(事件发生的)时间”。例如:Tell me the when and (the) where of it.(把这事的时间和地点告诉我。)

现在完成时态,是过去发生的事情,强调对现在造成的影响,和过去没有关系的,when翻译成什么时候,强调过去什么时间做了什么,对于现在没有直接的关系。 如:When did you mend your computer? -- yesterday 此句子是说明过去时间做的一件事情,对现在没有造成影响。

如How long have you been here? Three days 你到这里多长时间了? 三天了。 这个句子里用现在完成时态,强调过去到这里一直持续到现在。

when 引导的特殊疑问句 除了完成时态,其他时态都可以,具体要看你问的是什么时间的事情,然后判断好谓语就可以了。 因为提问的是时间,所以在问句中不用时间状语。

仅供参考, 祝学习进步!

有when的句子

副词 ad.1.(用作疑问副词)什么时候,何时I'd like to know when they'll let him out.我想知道他们什么时候放他.When did you last see Margaret?你上一次见到玛格丽特是什么时候?2.(用作关系副词,引导关系从句)当...时There were times when I didn't know what to do.有些时候我不知道该怎么办才好.连接词 conj.1.当...时John got engaged to her when travelling last winter.去年冬天旅行时,约翰与她订了婚.Don't get excited when you talk.你说话时别激动.2.既然,考虑到How can he get the promotion when his boss dislikes him?既然上司不喜欢他,那他怎么会获得提升呢?3.虽然,然而I had only fifteen dollars on me when the book I wanted cost twenty.我身上只带了十五元钱,可是我想买的那本书定价二十元.4.在那时,然后代词 pron.1.什么时候,那时Since when has she taught here?她从什么时候开始在这儿教书的?

含有when的句型,主句从句怎么用?比如,I often feel relaxed when ...

不一定,要看主句的时态,或者表述的具体意思,比如:I want to be a doctor when I grow up.这里就不是用过去时,因为when后面表示的是将来要发生的事。

I saw him sitting when I went in the house.这个句子when后面的动作跟主句里的saw是同时发生在过去,所以用过去时。

sql 的case when 语句

把括号去掉就好了。

下面是case的两种用法,可以看下 :1. 使用带有 CASE 简单表达式的 SELECT 语句。

在 SELECT 语句中,CASE 简单表达式只能用于等同性检查,而不进行其他比较。

下面的示例使用 CASE 表达式更改产品系列类别的显示,以使这些类别更易于理解。

USE AdventureWorks2008R2;GOSELECT ProductNumber, Category =CASE ProductLineWHEN 'R' THEN 'Road'WHEN 'M' THEN 'Mountain'WHEN 'T' THEN 'Touring'WHEN 'S' THEN 'Other sale items'ELSE 'Not for sale'END,NameFROM Production.ProductORDER BY ProductNumber;GO2. 使用带有 CASE 搜索表达式的 SELECT 语句在 SELECT 语句中,CASE 搜索表达式允许根据比较值替换结果集中的值。

下面的示例根据产品的价格范围将标价显示为文本注释。

USE AdventureWorks2008R2;GOSELECT ProductNumber, Name, 'Price Range' =CASEWHEN ListPrice = 0 THEN 'Mfg item - not for resale'WHEN ListPrice WHEN ListPrice >= 50 and ListPrice WHEN ListPrice >= 250 and ListPrice ELSE 'Over $1000'ENDFROM Production.ProductORDER BY ProductNumber ;GO

when的用法要有例句

1. QUEST 疑问词You use when to ask questions about the time at which things happen. 什么时候 (用于疑问句,询问某事发生的时间)例:When are you going home?你什么时候回家?例:When did you get married?你是什么时候结婚的?2. CONJ 连词If something happens when something else is happening, the two things are happening at the same time. (表示两件事同时发生) 当…的时候例:When eating a whole cooked fish, you should never turn it over to get at the flesh on the other side.吃一整条做熟的鱼时,你永远都不要把鱼翻过来吃另一边的肉。

3. CONJ 连词You use when to introduce a clause in which you mention something that happens at some point during an activity, event, or situation. 当…时 (引导从句,表示从句中提到的事发生在另一活动、事件或情况期间)例:When I met the Gills, I had been gardening for nearly ten years.我结识吉尔一家时,我已经几乎做了十年的园艺。

4. CONJ 连词You use when to introduce a clause where you mention the circumstances under which the event in the main clause happened or will happen. 在…情况下 (引导从句,表示从句中提到的情况是主句中已经发生或即将发生的事的前提)例:When he brought Imelda her drink she gave him a genuine, sweet smile of thanks.当他给艾梅尔达拿来一杯饮料时,她给了他一个真诚、甜美、表示谢意的微笑。

5. CONJ 连词You use when after certain words, especially verbs and adjectives, to introduce a clause where you mention the time at which something happens. 什么时候 (用在某些词尤其是动词和形容词后,引导从句说明某事发生的时间)例:I asked him when he'd be back to pick me up.我问他什么时候回来接我。

6. PRON-REL 关系代词You use when to introduce a clause that specifies or refers to the time at which something happens. 当…的时候 (引导表示某事发生的具体时间的从句)例:He could remember a time when he had worked like that himself.他还记得当他 自己也像那样工作的那段时间。

7. CONJ 连词You use when to introduce the reason for an opinion, comment, or question. 既然 (用于引入观点、评论、或问题的原因)例:How can I love myself when I look like this?既然我这么一副样子,我怎么能爱我自己?8. CONJ 连词You use when in order to introduce a fact or comment which makes the other part of the sentence rather surprising or unlikely. 而 (引出令人吃惊的事实或评论)例:Our mothers sat us down to read and paint, when all we really wanted to do was to make a mess.我们的妈妈们让我们坐下读书、画画,而我们真正想要做的却是胡闹一阵。

句子中有when说明是什么时态?该怎么用?

when可当疑问副词,也可当关系副词.1. when当疑问副词, 一定是放在句首.例: When is the play going to start? 这场戏什麽时候要开始?2.when当关系副词, 用来修饰表时间的先行词, 可用来代替"时间介系词+which",如" at which, in which"例: Do you remember the day THAT I invited you out? 记得我邀你出去的那一天吗?=Do you remember the day WHEN I invited you out?=Do you remember the day ON WHICH I invited you out?=Do you remember WHEN I invited you out? (这里的when引导名词子句作受词用) 3.when(当.....) 主要用於强调事情发生的时间. 用在句首或句中意思并没有差别例: When her name was called, she stood up.= She stood up when her name was called.叫她名字的时候,她站了起来.但注意, when在句首, 两个句子之间要用逗号隔开, when在句中, 就是一个句子.

句子中有When用什么时态?:等您坐沙发呢!

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