There is an old story about a king and his daughter. The king asked his daughter how much she loved him. She said that she loved him as much as she loved salt. Her answer made the king sad. Salt is a simple thing, and it is very common. So the king thought his daughter didn't care about him. But the king was wrong. Salt might be common, but it is very important. Throughout history, salt has caused wars. So why do people care so much about salt?

    Salt has many uses. Our bodies need salt. If we don't have enough, our body can't work properly. We put salt on icy roads to make them safe. We also use salt to produce other products. Products like paper, glass, rubber and soap depend on salt. But for many years, salt's most important job was preserving(保存)food.

    Like other living things, most bacteria(细菌)that cause food to spoil need water to survive. Salt absorbs large amounts of water, so most bacteria cannot live in a salty environment. As a result, salt has the ability to preserve almost anything. For much of human history, this ability has made salt treasured. Every ancient culture from Egypt to China depended on salt. Even today, we compare hardworking, useful people to salt by calling them "the salt of the earth".

    For centuries, salt was also hard to get. The combination(组合)of usefulness andraritymade it extremely expensive. Since almost everyone needed salt, the salt trade was an important business. Salt could even be used like money. In fact, the word salary(工资)comes from the word salt. And valuable people are still described as being "worth their salt." Today, salt is easy to get. It is no longer expensive, but it is still both important and useful.