Before的用法：
一、 before用作連詞
1． before用作連詞時,意思是“在……之前；還沒來得及 …… 就”.例如：
Before she could move,she heard a great noise,which grew to a terrible roar.她還沒來得及動彈,就聽見有很響的聲音,接著就成了可怕的隆隆轟鳴聲.
Before I could say a word,she had stormed out of the room.不等我說一句話,她就沖出了房間.
Don’t count your chickens before they are hatched.不要高興得過早.
2． 用于It + be + 時間段 + before...句型中,意思是“在……之后才……”.例如：
It will be five years before I come back.
我五年后才能回來.
It was not long before the enemy was driven out of their country.不久之后,敵人就被趕走了.
如果主句中用否定式,則表示“不多久……就”.
It won’t be long before they understand each other.他們不久就會互相了解的.
3． 還有“趁……（還沒有）”之意.例如：
They are thinking of buying the house before the prices go up.他們正在考慮趁房價未漲時把房子買下來.
Do it before you forget it.趁早動手,以免忘了.
二、before用作介詞
before用作介詞時,可以指時間“earlier than在……之前”,也可以指位置“in front of在……之前”.例如：
There is nothing that has not been bitter before being ripe.凡事在成熟前,都是有苦味的.
Don’t put the cart before the horse.不要本末倒置.
He was brought before the judge.他被帶到法官面前.
三、before用作副詞
before用作副詞時,意思是“at an earlier time / in the past以前”.例如：
I’ve seen the film Titanic before.我以前看過《泰坦尼克》這部電影.
I have never seen such beautiful flowers before.我以前從未見過如此美麗的鮮花.
四、短語before long與long before的區(qū)別
before long是“很快,不久”的意思,可以用于各種時態(tài).例如：
Before long,he went to America.不久,他就去了美國.
I hope to see you before long.我希望不久后再見到你.
而 long before是“很久以前”的意思,一般用在過去時或過去完成時的句子里.例如：
She said she had read the novel long before.她說她很久以前就讀過這部小說.
That happened long before.那件事發(fā)生在很久以前