“it”可以指代一整个句子或从句吗？如“it would be expensive if we stayed in hotel”？

不需要。

appreciate后面借助it+if或when引导的状语从句，所构成的句型叫作客气语气，并不是虚拟语气，虚拟语气主要用来表示假设，而非客观存在的事实，所陈述的是一个条件，不一定是事实，甚至完全与事实相反。虚拟语气通过谓语动词的特殊形式来表示。

英语中的语气分为陈述语气、祈使语气、虚拟语气、疑问语气和感叹语气五类。虚拟语气表示说话者做出的假设而非事实，或难以实现的情况，甚至表达彻底相反的概念。此外如需表达主观愿望或某种强烈的感情时，也可用虚拟语气。

如：If I were a bird，I would be able to fly in the air如果我是一只小鸟，我就能在空中飞行。

英语中的语气分为陈述语气、疑问语气、祈使语气、虚拟语气四类。虚拟语是一种表示假设状态的句型，是一种特殊的动词形式；表示所说的话不是一个事实，而只是说话者的一种假设，主观愿望，建议，猜测或不大可能实现的空想。

1、与现在事实相反的虚拟语气——过去时：If he studiedharder，he might pass the exam（如果他努力学习，他可能通过考试了）

2、与过去事实相反的虚拟语气——过去完成时：If he hadmoney，he would buy a car（如果他有钱，他会买辆车）

3、与将来事实相反的虚拟语气——主句用过去时：If it should rain，the game would be put off（如果下雨，比赛会推迟）

这个句子只能用whether,不能用if的原因是whether可以引导带to的不定式，if则不能。

我详细地列出来,你看看

whether和if都可以引导宾语从句，表示“是否”，在口语或间接引语中两者可以互换使用。如：

I wonder if / whether I can get some advice from you

Ask him whether / if he can come

但在有些情况下，whether和if的用法有一定区别。

1 whether引导的从句常可以与连词or或or not直接连用，而if一般不能。如：

正： Let me know whether you can come or not

误： Let me know if you can come or not

2 当宾语从句提到句首时，只能用whether引导，而不能用if。如：

正： Whether it is true or not, I can’t tell

误： If it is true or not, I can’t tell

3 whether可以引导带to的不定式，if则不能。如：

正： I don’t know whether to accept or refuse

误： I don’t know if to accept or refuse

4 whether及其引导的成分可放于介词之后，作介词的宾语，但if不能。如：

正： I worry about whether I hurt her feelings

误： I worry about if I hurt her feelings

5 whether可以引导从句，作主语、表语或同位语，而if不能。如：

正： It was uncertain whether he would come

误： It was uncertain if he would come

正： His first question was whether Tom had arrived yet

误： His first question was if Tom had arrived yet

正： We must consider the question whether we will take these measures

误： We must consider the question if we will take these measures

先纠正一下，it作形式主语时并不是可以替代主语从句，而是仅处于主语位置上的一个无含义的代词。这时it并不能代替任何从句或任何词。

本句中的it是主句的主语，if引导的是条件状语从句。it可以表示价格，这是它的用法之一。如"it is 100 dollars"。

It的用法（专项总结）

一、人称代词

1，it的最基本用法是作代词，主要指刚提到的事物，以避免重复:

①They watched the train until it disappeared in the distance

2，也可以指动物或婴儿(未知性别的婴儿或孩子):

②Is this your dog？No, it isn’t

③They got a baby and it was a ten-pounder

3，也可指抽象事物或指抽象环境和情景:

③I hate it when people talk with a full mouth．

二、非人称代词

1it有时并不指具体的东西而泛指天气、时间、日期、距离、价值、度量、温度、环境等：

⑴指天气：It is a lovely day, isn’t it ⑵指时间: It was nearly midnight when she came back

⑶指日期:It is April First today ⑷指距离:It is some 3000 kilometers from A to B

⑸指价值:It is three dollars ⑹指温度:Today it is 30 degrees centigrade

三、其他用法

1在句子的主语不太明确时充当主语，表示谁在做某事：

①Who is it there It's I (me/you/he) ②I thought it was Mary, but it was not she

③Her face lighted when she saw who it was

2泛泛的指某件事： (有时泛指一般情况)

①It doesn’t matter ②It is a shame, isn’t it ③How is it going(情况怎样)

④It says in the newspaper that

3it用在一些词组中，it 没有特别的意思

The last train's gone Come on, we'll foot it(来，咱们步行吧。)

四、作形式主语，替代主语从句，动词不定式，或动名词短语：　

1作形式主语替代主语从句

⑴It is clear ( obvious， true， possible， certain) that 从句 常译为＂┅清楚的（显然的，真的，可能的,肯定的．．．）＂

It is very clear that he’s round and tall like a tree = That he’s round and tall like a tree is very clear

⑵It is important ( necessary， right， strange， natural) that 从句 常译为┅是重要的(必要的,对的,奇怪的,自然的┅)that 后的从句中要用虚拟语气（should + 动词原形），should 可以省去，建议记住该句型中的形容词。

①It is important that we (should) learn English well②It is necessary that he (should) remember these words

⑶It is said (reported/ learned/believed/thought/known/told/hoped) that 从句 常译为＂据说（据报道，据悉．．．）＂。

①It is said that he has come to Beijing ②It is reported that another earth satellite has been put into orbit

⑷It is suggested ( advised/ ordered / demanded/ insisted/ commanded ) that 从句that　后的从句要用虚拟语气（should + 动词原形），should 可以省；常译为＂据建议；有命令．．．）

①It is suggested that the meeting ( should ) be put off

②It was ordered that we ( should ) arrive there in two hours

⑸It is time ( about time ，high time ) that从句(虚拟语气:动词用过去时did)

① It is time that children went to bed

⑹It is the first ( second ) time that从句(从句用现在完成时 have done )

It was …(从句用过去完成时had done )常译为＂是第一（二）．．．次．．．＂。

It is the first time I have been here = This is the first time I have been here

⑺It is a pity ( a shame /an honour/a good thing/a fact,/a surprise/ ) that从句

that后的从句一般用虚拟语气（should + 动词原形），should可省去．表示出乎意料，常译为＂竟然＂。没有这种意义时，则不用虚拟语气。

①It is a pity that such a thing ( should ) happen in your class 这种事竟然发生在你们班上，真是遗憾！

②It is a pity that he is ill 他生病了，真遗憾！

⑻It happens (seems， looks， appears ) that从句常译为 “ 碰巧…,似乎是…,看起来…”

①It happened ( so happened ) that he met his teacher in the street 碰巧．．

②It seems that he will be back in a few days 看来．．．

2作形式主语替代不定式　

⑴ It is kind ( of sb ) to do sth 不定式的逻辑主语是由 of引起，主句中的形容词必须是能表示逻辑主语特征的褒义或贬义形容词。 常见的词有：

bad ， brave ， careless， clever ， cruel ， foolish ， good （好心的）， honest ， horrible ， kind ， lazy ， modest ， naughty ， nice（有教养的）， polite， rude ， silly ， stupid ， wise ， wrong（错误的）等。 这个句型可以改写为：sb is kind to do sth 。　 如:It is kind of you to say so = You are kind to say so

⑵It is necessary ( for sb ) to do sth 不定式的逻辑主语是由for引起，主句中的形容词通常是表示重要性，紧迫性，频繁程度，难易，安全等情况的中性形容词。 常见的形容词有：

important， necessary， natural easy ， safe ， common ， normal ， hard ， difficult ， dangerous ， unusual， rare ， impossible ， pleasant

如:It is important for her to come to the party = It is important that she (should ) come to the party

⑶It takes sb to do sth 常译为＂做．．．要花费某人．．．＂。

如:It took thousands of people many years to build the Great Wall

3作形式主语替代动名词短语

It is no good / no use / useless doing sth 常译为 “┅有好处或没有用”

①It is no good learning English without speaking English

②It's useless trying to argue with Shylock

五、作形式宾语，代替不定式，动名词短语或宾语从句。

We think it important to learn a foreign language

该句型中的it 作形式宾语，该结构中常用的动词有：think, believe, make ,find consider, feel； 如:

We think it our duty to clean our classroom every day

He felt it important learning English well

They found it difficult that they would finish their work in two days

The Internet makes it easier for companies to keep in touch with customers

CF: keep sth, in mind / keep in mind that

六、it的重要句型

1强调句型: It is/was + 被强调部分 + that 从句 (被强调的主语如果是人，that可以由who换用)

①It was about 600 years ago that the first clock with a face and an hour hand was made

②It was they that (who ) cleaned the classroom yesterday

特例:It is not until + 被强调部分 + that 该句型也是强调句型。主要用于强凋时间状语，译成汉语＂直到．．．才．．．＂，可以说是 not until 的强调形式。

It was not until she took off her dark glasses that I realized she was a famous film star

it seems that:似乎,看来好像

例句 Sentences

It seems that

看来就是这样

It seems that she is ill

她似乎病了

It seems that it is going to rain

仿佛天要下雨

It seems to me that

在我看来

It seems(that) you were lying

看来你在撒谎

it seems as if:看来好像

例句 Sentences

It seems as if it were autumn

现在仿佛是秋天似的

It seems as if it were spring already

似乎春天已经来了

It seems as if he knew everything

好像他什么都知道似的

It seems as if Ken will win the race

看上去肯好像能赢

It seems as if she had been to England

好像她到过英国似的

it seems as if 那看上去好象常用虚拟语气

it seems that固定句型,那看上去如何如何,表事实

回答者：永远的2x9 - 举人 四级

It seems that American fast food is the most popular in the worle看来美国的快餐是世界上最受人欢迎的在这个句子里It seems that…是一个固定句型,“看来,似乎是,好像”的意思

例如：It seems that she is happy她似乎很高兴

It seems that he likes his new job他看起来很喜欢他的新工作

It seems that they don't like the idea他们似乎不喜欢这个主意

It seems that…句型也可以转换成 名词或代词 ＋ seem ＋ 动词不定式的句型,其原意不变如果动词不定式为to be ＋ 形容词时,to be往往省略例如：

American fast food seems to be the most popular in the world

看来美国的快餐是世界上最受人欢迎的She seems to be happy

她似乎很高兴He seems to like his new job

他看起来很喜欢他的新工作

They don't seem to like the idea他们似乎不喜欢这个主意

一、as if 从句的作用 1． 在look,seem 等系动词后引导表语从句如：She looks as if she were ten years younger． 她看起来好像年轻了十岁It seems as if our team is going to win． 看来我们队要胜了2． 引导方式状语从句如：She loves the boy as if she were his mother． 她爱这男孩,就好像她是他的母亲一样The child talked to us as if he were a grownup． 那孩子跟我们谈起话来,像个成年人似的二、as if 还可用于省略句中 如果as if 引导的从句是“主语＋系动词”结构,可省略主语和系动词,这样as if 后就只剩下名词、不定式、形容词（短语）、介词短语或分词如：He acts as if （he was） a fool． 他做事像个傻子Tom raised his hands as if （he was going） to say something． 汤姆举起手好像要说什么She left the room hurriedly as if （she was）angry． 她匆忙离开房间好像生气的样子三、as if 从句的语气及时态 1． as if 从句用陈述语气的情况当说话者认为句子所述的是真实的或极有可能发生或存在的事实时如：It sounds as if it is raining． 听起来像是在下雨He talks as if he is drunk． 从他谈话的样子来看他是醉了2． as if 从句用虚拟语气的情况当说话人认为句子所述的是不真实的或极少有可能发生或存在的情况时从句虚拟语气动词时态的形式如下：（1）如果从句表示与现在事实相反,谓语动词用一般过去时如：You look as if you didn’ t care． 你看上去好像并不在乎He talks as if he knew where she was． 他说话的样子,好像他知道她在哪里似的（2）从句表示与过去事实相反,谓语动词用“had＋过去分词”如：He talks about Rome as if he had been there before． 他说起罗马来好像他以前去过罗马似的The girl listened as if she had been turned to stone． 那女孩倾听着,一动也不动,像已经变成了石头似的（3）从句表示与将来事实相反,谓语动词用“would／could／might＋动词原形”如：He opened his mouth as if he would say something． 他张开嘴好像要说什么It looks as if it might snow． 看来好像要下雪了

回答者：bright1132 - 高级魔法师 七级

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