Why do people wear watches when they cross the desert?

　　腦筋急轉彎最早起源于古代印度。就是指當思維遇到特殊的阻礙時，要很快的離開習慣的思路，從別的方面來思考問題?，F(xiàn)在泛指一些不能用通常的思路來回答的的智力問答題。腦筋急轉彎分類比較廣泛：有益智類，搞笑類，數(shù)學類，成人類等。 腦筋急轉彎是種娛樂方式，同時也是一種大眾化的文字游戲。

　　1、What is it that is not burnt in the fire, and can't be drowned in the water?

　　2、I tell heat, and I tell cold, and they in turn tell me to go up and down as I am told. What am I?

　　3、Why do people wear watches when they cross the desert?

答案：

　　1、Ice.

　　2、The mercury in a thermomether.

　　3、Because watches have springs in them.