1、because（因爲），so（所以）不能同時出現在一個句子裏，只能用其一。
Because he was tired，he couldn’t walkt here.
=He was tired，so he couldn’t walk there.
因爲他累了，所以他不能走到那兒了。
2、（al）thouthg(雖然)，but(但是)不能同時出現在一個句子裏，只能用其一。但thouthg和yet可以同時出現在一個句子裏（yet用作副詞）
Thought he was tired，he still worked hard.
=He was tired，but he still worked hard.
雖然他很累，但他仍然努力工作。