... when/as/while ...
結構︰主要子句+when/as/while+子句
說明︰此句型意為“當…時”。when 引導的<子句>，不僅說明一般時間，而且可以表示與<主要子句>同時或提前的動作時間。兩個<動詞>常用現在式。as 所表示的同時意義更突出一些，語意更強一些;while 多指動作的過程，時間範圍較大一些。<連接詞> while 後面的<主詞>，如果與<主要子句>的<主詞>相同時，while 後面的<主詞>與 be <動詞>可以省略，如例句8。
When I got there, they were having a negotiation. 我到那裡時，他們正談判。
When I called, Tom was having dinner. 當我打電話時，湯姆正在吃晚飯。
When I met Jill, she was talking to a young man.當我遇到吉爾時，她正在和一個年輕人說話。
When I entered the room, everyone was laughing loudly.
當我走進房間時，每個人都在大聲地笑。
When you walk into the room, the lights turn on by themselves.
每當你走入這房間，電燈自己就打開。
The customer laughed as he spoke. 客戶邊談邊笑。
Work while you work, and rest while you rest. 工作的時候工作，休息的時候休息。
While she was reading in the room (=While reading in the room), she heard John call her.
當她在房間裡看書時，她聽見約翰在叫她。

... before/after ...
結構︰主要子句+before/after+子句
說明︰此句型意為“…之前/之後”。<主要子句>的動作發生在<子句>動作之前或之後。before 引導的<子句>不可用否定式。
You must send some sample to the customer before you go abroad.
在你出國之前，應該先寄給客戶一些樣品。
After you think it over, please let me know by fax. 你仔細考慮過之後，請用傳真相告。
What do you want to do after you have concluded this transaction?
這筆生意成交之後你想做什麼?

... because/as/since ...
結構︰主要子句+because/as/since+子句
說明︰此句型意為“…因為…”。because 作“因為”解釋，是<連接詞>，它後面所引導的<子句>，叫做“<從屬子句>”。<主要子句>前切不可加 so;<從屬子句>可放在<主要子句>後，但為了強調，可放在<主要子句>前。
I didn’t like it because it was noisy. 我不喜歡它因為很吵鬧。
His boss looked at him coldly because he made several big mistakes.
他的老板冷漠地看著他因為他犯了幾個大錯誤。
John lives happily because he uses his time well to study.
約翰生活得快樂因為他善用他的時間學習。
As rain has fallen, the goods cannot be shipped. 因為下了雨，貨物不能裝