2. 用作關(guān)系代詞，主要用法有二。如：
(1) 用在such, same, as等之后，引導(dǎo)限制性定語從句。如：
This is thesame watch as I lost. 這塊表跟我丟失的那塊一樣。
Such men as (=Those men who) heard of him praised him. 聽說過他的人都贊揚(yáng)他。
(2) 單獨(dú)用作關(guān)系代詞，引導(dǎo)非限制性定語從句，可放在主句之前 (常譯為：正如)或之后 (常譯為：這一點(diǎn))，且主從句之間一般要用逗號(hào)隔開。如：
He was absent, as is often the case. 他缺席了，這是常有的事。
As was expected, he succeeded at last. 正如我們所料，他終于成功了。
3. 用來表示目的，下面兩種句子結(jié)構(gòu)都可以。如：
仔細(xì)寫以便把每句話都寫清楚。
正：Write carefully so as to make every sentence clear.
正：Write so carefully as to make every sentence clear.
4. 在正式文體 (尤其是文學(xué)體裁)中，as后可用倒裝語序表示“…也一樣”這類意思 (現(xiàn)代英語通常so表示這一用法)。如：
He travelled agreat deal, as did most of his friends. 他去過許多地方旅游，他的多數(shù)朋友也是一樣。
He plays the piano, as does his mother. 他會(huì)彈鋼琴，他母親也會(huì)。
注：用作連詞，表示原因 (參見because)，表示時(shí)間 (參見when)。
5. 用于 as if
as though, 意為“仿佛”、“似乎”。兩者一般可通用 (但注意不能說 as although)。用法上注意幾點(diǎn)：
(1) as if [though] 可引導(dǎo)狀語從句和表語從句，從句謂語根據(jù)語義的要求，可用陳述語氣 (若可能為事實(shí))或虛擬語氣 (若為假設(shè)或不太可能是事實(shí))。如：
It looks as if it is going to rain. 天似乎要下雨了。
It seems as if you’re right. 似乎你是對(duì)的。
He talks asthough he knew everything. 他夸夸其談，好像無所不知。
When apencil is partly in a glass of water, it looks as if it werebroken. 當(dāng)把一支鉛筆的一部分放在一杯水里時(shí)，它看起來好像折斷了似的。
當(dāng)主句謂語是過去時(shí)態(tài)時(shí)，從句謂語�？捎藐愂稣Z氣。如：
He pausedas though he found a difficulty. 他停了下來，似乎遇到了一個(gè)難題。
She felt as if she lost something. 他覺得似乎丟了什么東西。
(2) 當(dāng)從句主語與主句主語一致，且從句謂語中又包括有動(dòng)詞be時(shí)，從句主語及其謂語中的動(dòng)詞be通�？梢允∪ァＨ纾�
From time to time heturned round as though (he was) searching for someone. 他不時(shí)地四下張望，好像在找人。
He opened his mouth as if (he was)to speak. 他張開口，好像要說話似的。
6. 關(guān)于 as…as, 用法注意：
(1) 中間只能用形容詞或副詞的原級(jí)，不能用比較級(jí)或最高級(jí)。如果在第二個(gè)as之后使用獨(dú)立的人稱代詞，一般說來用主格 (較正式)或賓格 (非正式)均可。如：
He’s as old as she
her. 他年紀(jì)跟她一樣大。
注意：
要是第二個(gè)as之后的人稱代詞跟有謂語動(dòng)詞，則該人稱代詞只能用主格。如：
He is as old as she is.
但是有時(shí)用主格或賓格含義差別很大。如：
You love him as much as I (=as I love him). 你愛他像我愛他一樣。
You love him as much as me (=as you love me). 你愛他像愛我一樣。
(2) 在肯定句中用as…as, 在否定句中用not as…as或not so…as 均可。如：
He doesn’t study as [so] hard as his brother. 他學(xué)習(xí)不如他弟弟努力。
(3) 要注意比較對(duì)象的一致性，即比較的雙方必須是可以比較的的同類人或物，否則會(huì)出錯(cuò)。如：
正：The population of China is much larger than that of Japan. 中國(guó)人口比日本人口多得多。
誤：The population of China is much larger than Japan.
(此句錯(cuò)在將 the population of China 與 Japan 來比較，比較對(duì)象不一致)
(4) 如果涉及數(shù)量或程度，可用以下兩個(gè)結(jié)構(gòu)。如：
①as much＋ (不可數(shù)名詞＋) as
�、赼s many＋ (可數(shù)名詞復(fù)數(shù)＋) as
You must speak English as much as possible. 你必須盡可能地多說英語。
You’ve made as many mistakes as I have. 你犯的錯(cuò)誤和我犯的一樣多。
(5) 請(qǐng)注意下列結(jié)構(gòu)的詞序。如：
她和她媽媽一樣是位好廚師。
正：She is a cook as good as her mother.
正：She is as good a cook as her mother.
誤：She is as a good cook as her mother.
(6) 修飾as…as結(jié)構(gòu)的常見詞語有nearly, almost, just, exactly, half, quite, twice, three times等，請(qǐng)注意這些修飾語都只能放在as…as 結(jié)構(gòu)之前 (而不能置于其中或其后。如：
This rope is twice aslong as that one. 這根繩子比那根長(zhǎng)一倍。
(7) as…as結(jié)構(gòu)的下列用法，屬于“異質(zhì)比較” (注：主、從句的主語和謂語一致時(shí)，從句的主語和謂語有時(shí)可以省略)。如：
The room is aslong as (it is) wide. 這房間的長(zhǎng)寬尺寸一樣。
The news was asunexpected as (it was) welcome. 這消息來得突然，但受人歡迎。
She is as clever as (she is) beautiful. 她既聰明又漂亮。
Oneis as light as the other is heavy. 一個(gè)輕，另一個(gè)重。
(8) as…as結(jié)構(gòu)在一定的上下文中可以用其省略結(jié)構(gòu) (即省去其中的一個(gè) as)。如：
She’s clever, but her brother is just as clever. 她很聰明，但她兄弟也一樣聰明。
The woman married a man pooras herself. 這個(gè)女人嫁給了一個(gè)與她一樣窮的男人。
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