YET和BUT的区别是什么,为什么THOUGH可以和YET连用,但不能与BUT连用

Though是“虽然”没错，但你不能用中文去理解，中文虽然followed by但是 当然是正确。

举例吧：Although it is wrong to kill someone, yet it is not guilty if you were acting from self-defense. (Though不能开头这个你知道吧)

同一句话也可以这样说：it is wrong to kill someone,but it's acceptable by law if you were acting from self-defense. 不能用although.

词性不同yet是副词,but是连词.
连接2个分句只需一个连词,though本身也是连词所以不能与but 连用.