替代詞one與the one的用法區別

one 用作替代詞主要用于替代“a＋單數可數名詞”，表泛指；若需特指，則用 the one。如：

A fast train is one that goes fast. 快車是一種行駛快的火車。

The accident was similar to one that happened in 2008. 這個事故與發生在2008年的事故類似。

Open the drawer on the left, the one with a key in it. 打開左邊的抽屜，上面有鑰匙的那個。

Here are six rings. Pick out the one you like best. 這里有六枚戒指，選出你最喜歡的一枚。

I want very much to see these films, especially the one you mentioned. 我很想看這些電影，特別是你提到的那一部。

注：the one與that均可表特指，但前者只用于替代單數可數名詞，而后者則可用于替代可數或不可數名詞。