急~~~~~~~~请教

when就是最一般的“当”，而as有随着的意思！
As he works harder and harder, his saving increases.
除此之外，when还有“此时”eg：I was walking in the street when a friend of mine called me.
as的意思比较多，主要有：因为，作为， 当，就像，在定语从句当中还有“正如”。
由于您要简单，所以不另举例子了！

when 是做为问句开头,
as 是做为后面回答