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
