though；although；as
这三个词都可以表示“虽然”、“尽管”。though和although引导让步状语从句时，常可互换，只是although的语气更强一些。如：
Though／Although it was late，the farmers kept on harvesting the crops by the lights of the tractors．
此外，though可以用于省略句，although很少这样用though引导的从句可以部分倒装，although引导的从句不用倒装语序。如：
Though poor, he is always neatly dressed．
Poor though I am, I can afford it．
as表示“虽然”、“尽管”引导让步状语从句时，从句要用倒装语序，将表语、状语等置于句首。
Tired as he was, he went on working with his workmates．
Child as he is, he knows a lot about the computer．
注意：as引导让步状语从句时，若充当表语的名词位于句首，则该名词前面不用冠词。
