从前有个人,他养了一只鹰,后来这鹰逃走了。几天后,在山上发现了鹰的尸体。主人想不出为什么鹰会无缘无故的死,在守林老人的指引下,他剖开鹰腹,才恍然大悟。原来鹰在笼中,养尊处优,竟失去了猎食的能力,腹中空空如也,活活饿死了。(点评:用故事形式开头,揭示自然界中存在的现象: Once there was a man, he raised an eagle and later the eagle escaped. A few days later, the eagle’s body was found on the mountain. The owner could not think of why the eagle would die for no reason. Under the guidance of the old man who was guarding the forest, he cut open the eagle’s abdomen and realized it. The original eagle in the cage, pampered, has lost the ability to hunt, empty stomach empty, starved to death. (Comment: Starting with a story, revealing the phenomena that exist in nature: