1. 替代单数可数名词时,均可用; 替代不可数名词时,不能用 the one,而要用that。比如:The weather of Beijing is colder than that of Guangzhou. 北京的天气比广州冷。(天气不可数)Your dictionary is more useful than the one my uncle gave me. 你这本词典比我叔叔给我的那本词典更有用。(词典为可数)2. 替代事物时,均可用; 替代人时,只能用 the one。比如:—Who is her husband? 哪位是她的丈夫?—The one by the window. 窗户边的那一位。注:当要替代性别不明的婴儿时可用 it。3. 当有前置定语修饰时,只能用 the one。比如:—Which do you want? 你想要哪个?—The red one. 那个红的。She would rather have the small one than the large one. 她宁愿要小的,不要大的。4. 当有后置定语修饰时,通常用 the one。比如:My room is better than the one next door. 我的房间比隔壁房间好。Here are six rings. Pick out the one you like best. 这里有六枚戒指,选出你最喜欢的一枚。但是,若后置定语为 of 引起的介词短语,则通常用 that。如:The population of China is much larger than that of Japan. 中国人口比日本人口多得多。A grandparent’s job is easier than that of a parent. 祖父母的任务比父母的任务要轻松一些。