preamble bit

例句：

1. 1. The book begins with a preamble explaining its purpose.
   这本书以序言开始，解释了其目的。
2. 2.The meeting began with a preamble about the agenda.
   会议以关于议程的序言开始。
3. 3.The author's preamble sets the tone for the rest of the work.
   作者的序言为作品其余部分定下了基调。