as 引导让步状语从句应注意什么?

as引导让步状语从句时,状语表语及谓语动词的一部分置于as之前,且表语
中的冠词要省略。如：Try as we did we failed again。又如：Late as he
came he saw the famous man。而although则无此种用法,句中although应改为 as。
as引导让步状语从句时,常放在作表语,状语或谓语的一部分的形容词,名词,副词或动词原形之后。如果是单数名词或形容词的最高级作表语,不再用冠词。
however和as 引导让步状语从句时的区别：
however引导让步状语从句时,相当于no matter how,后面跟形容词或副词；as引导让步状语从句时,用倒装语序,即把作状语的副词或作表语的形容词或名词提前,而且如果作表语的是单数名词,前面不加冠词,也可以把谓语动词部分的实义动词提前。
〔误〕 As hard he works,he can’t catch up with his classmates。
〔正〕 However hard he works,he can’t catch up with his classmates。
〔析〕见上述说明。
〔误〕 A model worker he is,he remains modest。
〔正〕 Model worker as he is,he remains modest。
〔析〕as 引导让步状语从句,前面的单数名词前不加冠词。