先行词

例句：

1. 1. The first question is the most important one.
   第一个问题是最最重要的。
2. 2. She asked for an appointment with her boss before she left.
   她离开前要求与老板预约。
3. 3. The book was given to him as a gift before he arrived at the party.
   这本书在他到达派对之前作为礼物交给他了。