Thirty years ago, most teenagers had bicycles, but now they are comparatively rare. 【C1】______ , motor scooters(小型摩托车)are much more common. 【C2】______ , this may seem to be a sign of progress but 【C3】______ the change is not necessarily for the better. It is easy to see why young people prefer scooters. 【C4】______ , they are much faster and do not require much physical effort 【C5】______ , you can take a passenger with you on the pil-lion(后座)seat behind 【C6】______ , they give young people a feeling of independence, be-cause they can travel further and impress their friends. 【C7】______ , the disadvantages are equally obvious. 【C8】______ first sight, scooters are more expensive to buy and to maintain, and 【C9】______ those under 16 are not allowed to have them. 【C10】______ , greater freedom brings danger because speed encourages young people to take risks and as a result scooters are in-volved 【C11】______ more accidents, and the accidents are 【C12】______ more serious. Bicycles are safer and easier to control. Years ago, teenagers had more experience with them because they 【C13】______ to ride as young children, and consequently knew what they were capable of. 【C14】______ , many young people overestimate what a scooter can do and pre-tend it has the power of a motorcycle. 【C15】______ , the fact is that bicycles are not very safe 【C16】______ in cities these days because there are more cars and drivers are not used to them and do not make allowances for them. 【C17】______ , those who are old enough to ride scooters naturally prefer them. Those who are too young or cannot afford to buy a scooter probably find bicycles glow and uncomforta-ble 【C18】______ , and riding bicycles requires 【C19】______ experience of traffic than before. On bal-ance, the change has been for the worse, 【C20】______ for the 13-and 14-year-olds, but the only safe solution would be to have special lanes(车道)for cyclists. 【C1】______