“Plants are the basis（基础）of all life, including ourselves. We depend on them for every mouth of food that we eat and air that we breathe,” said David Attenborough in The Green Planet. It is plants that bring us fruit and vegetables. Plants also give us the air we need. Though they can’t walk or talk, they act like animals in many ways.

Every time you move, three body systems work together to help you. Your skeletal（骨骼的）system works with your muscular（肌肉的）and nervous（神经的）systems to help you run, jump, sit, walk, and swim.

Your skeletal system has more than 200 bones. It is a structure that supports your body and protects your inner body parts. Even though the bones are hard, they are still living tissues（组织）.

Your muscular system is made up of all the muscles in your body. Your skeleton could not move without muscles. You also need your muscular system to keep your posture.

The nervous system is the control centre for all of your body’s organ（器官）systems. It helps you to know the changes in you and around you. It helps you to react（反应）to your environment.

All of your muscle movements（运动）are controlled by your nervous system. The brain is the centre of your nervous system. Billions of nerve cells（细胞）make up the tissues of your brain. Each day, nerve cells in your brain send and get thousands of messages to and from the parts of your body. Of course, nerve cells are found throughout the body, not only in the brain according to the knowledge you have learned in biology.

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In 1957 a 10-year-old boy in California set a goal. At the time Jim Brown was the greatest player ever to play football and this tall, thin little boy wanted his autograph (亲笔签名).     16    

    17     He never got enough to eat for his family was very poor. Malnutrition (营养不良) injured his health, and a disease called rickets (佝偻病) forced him to wear steel splints (钢板) to support his bow-shaped legs.     18     What he could only do was that he waited patiently near the dressing room until the game ended. and Jim Brown left the field. He politely asked Brown for his autograph. As Brown signed, the boy said, “Mr. Brown, I have your picture on my wall. I know you hold all the records. You’re my idol (偶像).”

    19     He added, “Mr. Brown, one day I’m going to break every record you hold!” Brown was touched and asked, “What is your name, son?”

The boy replied, “Orenthal James. My friends call me O. J.”

    20     But O. J. Simpson went on to break all these records except three before injuries shortened his football career. Goal setting is the strongest force for human development. Set a goal and make it come true.