Why do people wear watches when they cross the desert?

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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.