有一下两个题干部分
Nancy is the only one of the visitors that is able to do that.
He is the only one of the foreign experts who is working in China.
请问老师是否在这样的情况下，不肯定只可以用that，我可以如此理解这种现象么？
谢谢老师。
当先行词有 only 修饰时，其后的定语从句用什么关系代词来引导，大致遵循以下原则：
1. 若先行词指事物，其后的定语从句一般用 that 来引导。如：
The only thing that keeps me awake is coffee. 能让我维持清醒的只有咖啡。
This is the only painting in this style that we have. 这种风格的画大家仅有这一幅。
但用 which 也不算错，只不过比较少见而已（建议学生考虑时不要如此用）。如：
Politics is the only thing which separates us. 大家只不过政治看法相左。
2. 若先行词指人，其后的定语从句既可 that 也可用 who 来引导。如：
He’s the only man that can do it. 他是唯一可以做这事的人。
Man is the only animal that has the faculty of speech. 人类是唯一有说话能力的动物。
He is not the only person who has to be considered 他并不是是唯一要考虑的人。
Harry is the only person who can do this trick. 哈利是唯一会这玩意儿的人。
