when, while, as

1. The Queen's last visit was in May, when she opened the new hospital.
   女王上次來訪是在五月份，她那時主持了這座醫(yī)院的落成典禮。
2. How can they learn anything when they spend all their spare time watching television?
   他們把所有的空閑時間都用來看電視了，還能學(xué)什麼東西呢？
3. It was the sort of morning when everything goes wrong.
   那天上午就是那樣，事事不順心。
4. It was raining when we arrived.
   我們到的時候正在下雨。
5. He was fond of drawing when he was a child.
   他還是個孩子時就喜歡畫畫。
6. Turn off the switch when anything goes wrong with the machine.
   如果機器出故障，就把開關(guān)關(guān)掉。
7. When did that happen?
   那件事是什么時候發(fā)生的？

when

adv.（副詞）
At what time:
什么時候：
例句：
When will we leaveô
我們什么時候離開ô

conj.（連接詞）
At the time that:
在…的時候：
例句：
in the spring, when the snow melts.
在春天，當(dāng)雪融化的時候

As soon as:
一…就…：
例句：
I`ll call you when I get there.
我一到那里就給你打電話

Whenever:
無論什么時候：
例句：
When the wind blows, all the doors rattle.
只要風(fēng)一吹，這門就吱嘎作響

During the time at which; while:
在…期間，當(dāng)…時：
例句：
When I was young, I was sick all the time.
在我小時候我總是生病

Whereas; although:
雖然，盡管：
例句：
She stopped short when she ought to have continued.
盡管她應(yīng)該繼續(xù)下去，她卻突然停住了

Considering that; if:
考慮到，如果：
例句：
How can he get good grades when he won`t studyô
他不用功的話怎么拿高分呢ô

pron.（代詞）
What or which time:
什么時候：
例句：
Since when has this been going onô
從什么時候起事情象這樣ô

n.（名詞）
The time or date:
時間或日期：
例句：
Have they decided the where and whenô
他們已經(jīng)定下來地點和時間了嗎ô

來源：
Middle English
中古英語
from Old English hwenne * see k wo-
源自 古英語 hwenne *參見 k wo-

In informal stylewhen is often used after be in definitions: A dilemma is when you don`t know which way to turn. The construction is useful,but it is widely regarded as incorrect or as unsuitable for formal discourse.In formal style there is no alternative but to rephrase such definitions to avoidis when : A dilemma is a situation in which you don`t know which way to turn. You are in a dilemma when you don`t know which way to turn.
在非正式文體中when 常在定義中用在 be 后面： 進退兩難就是當(dāng)你不知道該走哪條路的時候。 這個結(jié)構(gòu)是有用的，但被廣泛認(rèn)為它對正式交談來說是不正確的或者是不合適的。在正式文體中沒有替代詞，只能改變措辭以避免is when ： 進退兩難就是這樣一個你不知道該怎么辦的處境。 當(dāng)你不知道你該做什么時你就處于進退兩難的維谷了