海水为什么是咸的？

Sea water tastes salty. 海水喝起来，是咸咸的。 But rain and rivers are not salty. 可雨水和河水，并不咸呀。 Rain washes salt off the land. 雨水把陆地上的盐分冲下来。 It carries the salt into rivers. 这些盐，就顺着河水流走。 All the rivers run into the sea. 江河最后，都汇进了大海。 The water goes away as steam. 水变成蒸汽飞走了。 But the salt stays, so the sea gets saltier. 盐却留下，大海就越来越咸啦。