as的用法
1、as做介词，意思是“作为”
例句：
French is known as the most beautiful language in the world.
法语以世界上最美丽的语言著称。
2、as做连词，引导时间状语从句，意思是“当……的.时候”
例句：
My mother was cooking fish as I arrived home.
当我到家的时候，我妈妈正在做鱼。
3、as做连词，引导原因状语从句，意思是“因为”
例句：
As rain has fallen, the air is cooler.
因为下过雨，所以空气比较凉爽。
4、as做连词，引导让步状语从句，意思是“虽然”
例句：
Young as he is, he has been one of the most famous painters in our country.
虽然他还很年轻，但已经成为我们国家最有名的画家之一。
5、as做连词，引导方式状语从句，意思是“以……方式”
例句：
Do as the Romans do when in Rome.
入乡随俗
6、as做关系代词，引导定语从句
例句：
This is the same game as I played yesterday.
这和我昨天玩的游戏一样。
though用作连词，有虽然，即使等含义。用作副词时，有不过，可是，然而等含义。though引导的让步状语从句可用部分倒装的形式。
though的用法
一、用作连词
表示“虽然”，although 比 though 更为正式：两者大致同义，可换用。
Though （Although）it was barely four o’clock, the lights were already on.
尽管才四点钟，灯已经亮了。
Though （Although）we are poor, we are still happy.
我们虽然穷，仍然很快活。
二、用作副词
though 可用作副词，一般放在句末(不放在句首)，意为“可是”、“不过”。
I like him. Though he makes me angry sometimes.
我喜欢他，不过他有时惹我生气。
三、用于倒装
though 引导的让步状语从句可用部分倒装的形式(注意：倒装后位于句首的名词之前不用冠词)