We all know that cycling is a great exercise. A doctor told me that people who live the longest are dancers and cyclists. Maybe it is because of the combination of fresh air, smooth movement and exercise. When you ride a bicycle, you don't use petrol. So they are not producing carbon dioxide and not causing air pollution. Just look at how cars have taken over our cities. They often run at high speeds and might put our lives in danger. And then there are traffic jams, too. Our cities would be better places if we replace cars with bicycle.