表示理由的關係副詞 why
例句：這是我不原諒他的原因之一。
未使用關代連接兩句時
This is the reason.使用關代連接兩句
I will never forgive him for the reason.
This is the reason which I will never forgive him for .改成說明理由的關係副詞：關係副詞 = 介係詞 + which
This is the reason for which I will never forgive him.
This is the reason why I will never forgive him.
