preliminary: refers to what must be done or prepared or acquired before some other state or activity becomes possible: held a ~ discussion to set up the agenda for the meeting.    （还表示预赛，如the winner of each preliminary goes through to the final. 每场预赛的获胜者进入决赛）


introductory: refers to the first steps in a process and usually applies to what sets something  (such as an action, a work, or a process) going: the speaker's ~ chapters established his point of view.   介绍性章节


preparatory: comes close to preliminary in meaning but emphasizes preparedness for or against what is expected to ensue: take ~ protective measures against a predicted hurricane.


prefatory: usually implies a desire on the part of someone to prepare others for such activities as hearing, action, or understanding, or process: made some ~ remarks before introducing the speaker.


preliminary预先: 指必需先进行否则后续无法开展的事情，introductory介绍: 指某过程最开始的部分，用于启动该过程(和preliminary不同，introductory是整体的一部分)，preparatory预备: 强调为接下来发生的事做好了准备，prefatory前言预备:  也表示做好准备，但是是使他人做好准备


记忆方法: 1）首字母PIPP想成我和三人<==预备


               2）预备的意思是为某事做好准备mean serving to make ready the way for something else.