①取研碎后的钙片4克，倒入气密性良好的锥形瓶中，然后在分液漏斗中加入适量的稀盐酸，置于电子天平上测出装置的总质量。

②打开活塞，滴入足量稀盐酸后关闭活塞，待气泡不再冒出时，测出反应后装置的总质量。

③整理相关数据如表所示，计算出钙片中碳酸钙的质量分数。

    We each have a memory（记忆力）. That's why we can still remember things after a long time. Some people have very good memories and they can easily learn many things in a short time, but some people can only remember things when they say or do them again and again. Many of the great men of the world have got surprising memories.

    A good memory is a great help in learning a language. Everybody learns his mother language when he is a small child. He hears the sounds, remembers them and then he learns to speak. Some children are living with their parents in foreign countries. They can learn two languages as easily as one because they hear, remember and speak two languages every day. In school it is not so easy to learn a foreign language because the students have so little time for it, and they are busy with other subjects, too.

    But your memory will become better and better when you do more and more exercises.