下雪天为什么要撒盐？

Snow covers the road on cold days. 天冷下雪，路面就白白一片。 People spread salt on the snow. 人们把盐撒在雪上。 Salt makes ice melt at a lower temperature. 盐能让冰在更低的温度下融化。 Pure ice melts at zero degrees. 纯水做的冰，零度就会化。 With salt, it needs a colder day to freeze. 加了盐，天更冷才会重新结冰。 So the road stays clear and safe. 路面化得快，走路开车都安全。 That is why salt comes out in winter. 所以一到冬天，盐就派上了用场。