1. when表疑问
When will they come back?
他们什么时候回来？
When does he take a shower?
他什么时候洗澡？
Since when have they had the house?
他们从什么时候起有这幢房子的？
Till when is the library open?
图书馆开放到几点呢？
2. when作连接副词
I'd like to know when they will come.
我想知道他们什么时候来。
Can you tell me when the bank opens?
你能告诉我银行什么时候开门吗？
When she'll be back depends much on the weather.
她何时回来在很大程度上取决于天气。
Have you decided when to go sightseeing?
你们已经决定什么时候去观光了吗？
3. when作关系副词
Do you remember the time when the three of us went on a picnic?
你还记得我们三个人去野餐的那段时光吗？
The days are gone forever when the Chinese people were looked down upon.
中国人民被人轻视的日子一去不复返了。
In the old days, when I was a little boy, the city had no industry to speak of.
以前，我还小时，这个城市没有工业可言。
The main school holidays are from mid-December till early February, when the days are long and warm.
学校的主要假期是从12月中旬到2月初，这段时间里白天长而且温暖。?
4. when引导时间状语从句
When you see him, please say hello to him.
见到他时，代我向他问号。
When I was in Japan, I bought some beautiful pearls.
我在日本时买了一些漂亮的珍珠。
When I reached the station, the train had left.
我到达火车站时火车已经开走了。