adj+as+主+系动词，主句 例：Young as he is, he knows a lot.
n（无限定词）+as+主+系动词，主句 例：Child as he is, he knows a lot.
adv+主+动词，主句 例：Fast as he runs, he can't catch me.
个人认为，这个让步状语从句不是倒装，而是提前，因为从句主谓还是正常语序的。
