2. Americans use a flashlight, while for the British, it's a torch.
美國人把手電筒稱作flashlight,而英國人則叫它torch。
句中while是并列連詞，連接并列句，意為“然而，而”，此處表示對比，并含有輕微的轉折意味。
在……過程中，在……期間 (=when)
while雖然，盡管 (=though)
只要 (=as long as)
Someone came to see you while you were out.
你出去時，有人來找過你。
There will be life while there is water and air.
只要有水和空氣，就會有生命。
While he was right, few people would follow him.
雖然他是正確的，但是沒有幾個人愿意聽他的。
注意：while 引導讓步狀語從句必須置于該從句的句首。

3. The other two areas in which the two varieties differ are spelling and pronunciation.
這兩種英語另外兩個領域的區別是拼寫和發音。
本句為主從復合句,in which 引導定語從句，修飾areas。
介詞+關系代詞引導定語從句的選擇：
根據從句謂語動詞的搭配習慣：
This is the dictionary/on which I spent 50 yuan./for which I paid 50 yuan./from which I learnt a lot./about which he often talks.
根據先行詞的搭配習慣：
I remember/the day on which I joined the league./the days during which I lived there./the month in which I stayed there.
介詞可后移，此時關系詞可省略：
The person/to whom we'll write./we'll write to.

4. When the Irish writer George Bernard Shaw made the famous remark that the British and the Americans are two nations divided by a common language,he was obviously thinking about the differences.
當愛爾蘭作家喬治•蕭伯納講那句名言——英國和美國是被同一種語言分開的兩個民族時，他顯然想到了它們的區別。
本句為主從復合句，when 引導了時間狀語從句,在此從句中又含有that引導的同位語從句。
同位語從句一般跟在某些名詞(如：fact, idea, news, promise, information, message等)的后面，用以說明或解釋前面的名詞。引導同位語從句的連接代詞that，連接副詞how, when, where等。
I have no idea when he will be back.
我不知道他何時回來。