What is this watch for?

题目

What is this watch for?
What did you do that for?
请教这里的for 有没有相关的例句呢,

答案

What is this watch for?这只手表是用来干什么的?
What did you do that for?你为什么要那样做?这里what for相当于why
for的意思一目了然