Why does the lemon taste sour? 为什么柠檬的味道很酸？

　　It is because of the acid in a lemon. 因为柠檬里有酸。

　　Then what is acid? 那么什么是酸？

　　All substances with a sour taste are kinds of acid. 所有带酸味的物质都是酸。

　　Vinegars, some fruits and car batteries have some acid. 醋，一些水果和汽车电池都有一些酸。

　　Acid can burn other substances when it meets them. 酸遇到其他物质时可以燃烧。

　　So you have to be careful when you use strong acid, because it can burn your skin. 所以你在使用强酸时要小心，因为它会灼伤你的皮肤。

　　Acid is important for people's health. 酸对人们的健康很重要。

　　Some acid plays an important role in cell maintenance and repair. 一些酸在细胞的维护和修复中起着重要的作用。

　　And the formation of red and white blood cells. 它对红血球和白细胞的形成也有作用。