as作连词的用法:
1、作,当的时候,引导时间状语从句。
例句:As a young man, he was active in sports。
2、as等于since,作既然。
例句:As he wasn't ready in time, we went without him。
3、作,虽然、尽管,引导让步状语从句。
例句:Tired as they were, they walked on。
as作关系代词的用