Tom has three good friends. They are Jack, David and Mark. They have different hobbies. Tom likes football. He often plays football on weekends. He thinks playing football can make him strong and healthy. He is in the school football team.

    Jack doesn't like sports. He likes listening to music. He likes Jay Chow best of all the singers. He has many of his CDs. He often listens to music on the way. He thinks music can let him feel happy.

    David doesn't like sports or music. He likes stamps. He collects stamps for five years. The stamps are very beautiful. He thinks collecting stamps can help him know more about the world.

    Mark likes taking photos. He has a few cameras. When he is free, he often takes out his camera and takes some pictures. Some of his pictures are in the newspapers. He thinks the world is beautiful. He wants to show the beauty of the world to others.

食物中的蛋白质到达胃中才开始进行化学性消化，这是因为胃腺能分泌（　　）

舒婷在《人心的法则》中写道：“为一个诺言而信守终生?为一次奉献而忍受寂寞?是的，生命不应当随意挥霍，但人心，有各自的法则。”这段诗句所包含的哲理是（  ）