HAVE you ever noticed that, in the summer, when your sweat dries it will leave marks on your T-shirt? The marks are tiny bits of salt.

• 你有没有注意到,夏天的时候,汗水干了之后会在T恤衫上留下一些痕迹?其实,这些痕迹是由极少量的盐留下来的。