the first to do为什么要用to do？ - 知乎 first 有多种词性，其中就有名词，剑桥词典对作名词的first的定义是：the first person or thing to do or be something, or the first person or thing mentioned，例句有： [ + to infinitive ] She was one of the first to arrive 和He is the first (= very willing) to admit that much of his success is due to his good looks