Many people in the world walk to work or to school. They have no other form of transportation. Many others, however, travel by bus, train or car. They walk very little. Yet experts say walking is one of the best ways to stay healthy. They call it the world’s most natural exercise. Walking is less dangerous than running. It strengthens the muscles without stretching them too much. And it puts less pressure on bones and joints(关节). About fifty million Americans are active in what is called “fitness” walking. They take fast and short walks a few times each week to improve their health. Fitness walking can be done almost anywhere, anytime. What’s more, no special equipment is needed. Experts advise drinking lots of liquids, especially water, before and after each walk. Also, gently stretch the muscles and joints that are most likely to become tense (紧张的,拉紧的)during the exercise. The most effective way to walk is the natural way. Keep your head high and your back straight. In fitness walking, it is important to remember that your footsteps should fall almost in a straight line. Bend your arms at the elbow. Let them swing from the shoulder with each step. Walking is not only good for your body but also for your emotional health. In an experiment, a group of students were first asked to describe their levels of energy and tension. Then they went on a fast walk for ten minutes. When the students returned, they reported feeling less tired and more full of energy. This pleasant feeling lasted at least one hour. Even after two hours, the students felt less tired than they had before the experiment. Fast and short walks can also help make personal problems seem less serious. One group of persons described the seriousness of their personal problems, such as job worries or a failing marriage. Then they went for a fast ten-minute walk. When they returned, they said their problems seemed less threatening. Improvements were not observed every day. But after three weeks, the differences became very clear. Of course, walking can’t solve your problems. But it can help you in many ways. So why not give your feet a little exercise from time to time? Read the sentences below and decide if they are true or false according to the text. Write T for true or F for false(判断正误).