The bicycle is one of the most important vehicles in the world. In every country people use bicycles for work, for sport or just for fun . Bicycle riding is good exercise. It helps people become fit. Bicycle riding can make the riders' hearts and lungs strong. It is also good for the environment because bicycles do not cause pollution. Bicycles share the road with cars and trucks. Drivers do not always notice bicycles. So bicycle riders must pay attention to the traffic around them and know traffic signals. They must know and obey the safety rules. They must wear helmets(头盔) to protect their heads. When riding at night, they must wear light-colored clothes, and have lights in the front and reflectors on the back of their bicycles. In a word,the best way to be safe is to be careful.