when在句中的意思,及所起的语法作用.

when在这个句子是连词,引导一个时间状语从句,修饰 “Saturdays and Sundays ”
第一种ad.（形容词）
1.(用作疑问副词)什么时候,何时
I'd like to know when they'll let him out.
我想知道他们什么时候放他.
When did you last see Margaret?
你上一次见到玛格丽特是什么时候?
There were times when I didn't know what to do.
有些时候我不知道该怎么办才好.
第二种adv.（副词）
1.[疑问副词]什么时候,何时
2.[关系副词]当...时
I still remember the night when Nanjing was liberated.
我还记得南京解放那天晚上的情景.
When will he come?
他什么时候来?
It was a time when motorcars were rare.
那是汽车很罕见的时代.
conj.
1.当...时
How can he get the promotion when his boss dislikes him?
既然上司不喜欢他,那他怎么会获得提升呢?
I had only fifteen dollars on me when the book I wanted cost twenty.
我身上只带了十五元钱,可是我想买的那本书定价二十元.
Don't get excited when you talk.
你说话时别激动.
John got engaged to her when travelling last winter.
去年冬天旅行时,约翰与她订了婚.
n.
1.(事件发生的)时间[the S]
pron.
1.&ad.什么时候
Since when has she taught here?
她从什么时候开始在这儿教书的?

when引导了一个定语从句
修饰 前面的先行词

Most newspapers have several sections, especially on Saturdays and Sundays （when the edition is longer than usual）.
括号内是定语从句，修饰Saturdays and Sundays .

当……的时候