in which & when的疑问~

lilingfeng

以前上XDF的时老师讲说   age用in which 修饰   ； time 具体年代用when修饰

但是今天看到OG12里的一道题目 His studies of ice-polished rocks in his Alpine homeland,far outside the range of present-day glaciers,led Louis Agassiz in 1837 to propose the concept of an age in which great ice sheets existed in what are now temperate areas.（正确的句子）

OG里面解释说In which or when can be used interchangeably in this sentence.

想知道为什么？ 那以后看句子是不是不能根据in which 和when直接排除了？？

liaoyoumin

【PERIOD OF HISTORY】 [C usually singular]
a particular period of history
　We are living in the age of technology.

朗文字典关于Age解释有这么一个。in the age，所以这道题可以用in which。OG也说了这个句子里他们是可以互换的

liaoyoumin

又查了一下，确切的讲，这道题里还是应该只用in which。

age后面可以跟in which 和when，不过这道题里的age应该是in的意思。

age前面可以跟in/at/of几个介词。

【HOW OLD】 [U and C]
the number of years someone has lived or something has existed
　　Dad retired at the age of 56.

at age 5/18 etc
　In Britain, schooling starts at age 5.
4/15 etc years of age
(=4, 15 etc years old)
　She was just over 16 years of age.

加上上面的in。

when可以=on which和at which，=in which还是少。

used after an expression of time to mean 'at which' or 'on which': Sunday is the only day when I can relax. ◆ There are times when I wonder why I do this job.
at which time; on which occasion: The last time I went to Scotland was in May, when the weather was beautiful.

所以这道题还需要讨论。

liaoyoumin

IN an age when the poultry industry of North America pays glowing tri- bute to the "Hen of the Year" and ...
The role of patient age when deciding to transfer at the blastocyst stage.

mingzhu

About "when" vs. "in which", an earlier comment demonstrated the correct usage:

I was 18 when...
It occured during an age in which...

Specific age should be "when", referring to a period of time should be "in which".