one 用作替代詞主要用于替代“a＋單數(shù)可數(shù)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(fā)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(shù)可數(shù)名詞,而后者則可用于替代可數(shù)或不可數(shù)名詞.
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.