as,though ,although这三个词的用法各有区别.具体来说,as引导的让步状语从句必须倒装;though引导的让步状语从句可以倒装也可以不倒装;而although引导的让步状语从句不能倒装.
e.g.Hard as he tried,he still failed.(他虽然努力了,但仍然失败了.)
Though he tried hard,he still failed.
Hard though he tried,he still failed.
Although he tried hard,he still failed.