Are you a man or a mouse? When people ask this question they want to know if you think you are a brave person or a coward . But you will never really know the answer to that question until you are tested in real life. Some people think they are brave, but when they come face to face with real danger, they act like cowards. Other people think of themselves as cowardly, but when they meet danger, they act like heroes. Lenny Sputnik had always thought of himself as a nervous person. He got worried before examinations. He worried about his job and his health. All he wanted in life was to be safe and healthy. Then, on 15th January 1982, a plane crashed into the Potomac River in Washington. Lenny went to the river to see what was happening. Then he saw a woman in the ice-cold water. Suddenly Lenny did not feel afraid. He kept very calm and did a very courageous thing. He jumped into the Potomac, swam to the woman, and kept her head above the water. Seventy-eight people died that day. Thanks to Lenny Sputnik, it was not seventy-nine. When you are in a very dangerous situation and feel afraid, the body automatically produces a chemical in the blood. This chemical is called adrenalin. With adrenalin in the blood system, you actually feel stronger and are ready to fight or run away. However, when you are completely terrified, the body can produce too much adrenalin. When this happens, the muscles become very hard and you find that you cannot move at all. You are then disabled with fear. That is why, when we are very frightened, we sometimes say that we are 'petrified'. This word comes from the Greek word 'peters' which means 'stone'. We are so frightened we have become like stone. Adrenalin in our body is   _  .
harmful useless changeable dangerous