There is a range of activities which require movements of about one to four or five miles.These might be leisure activities, such as moving from home to swimming pool, tennis club, the theater or other cultural centers, or to a secondary or more advanced school, or they might be movements associated with work and shopping in the central areas of cities.The use of cars capable of carrying five people at 80 mph for satisfying these needs is wasteful of space and most productive of disturbance to other road users.

　　The use of the bicycle, or some more modern derivative of it, is probably worth more consideration than has recently been given to it.The bicycle itself is a remarkably efficient and simple device for using human muscular energy for transportation.In pure energy terms, it is four to five times as efficient as walking, even though human walking itself is twice as efficient as the movement of effective animals, such as dogs or gulls.It is still widely used, not only in some developing countries where bicycles are major means of people and goods, but in a few richer towns such as Amsterdam in Holland and Cambridge in England.

　　It usually gives inadequate protection from the weather, is not very suitable for carrying goods, and demands considerable muscular work to make progress against wind or uphill.It also offers its rider no protection against collisions with other vehicles.All these difficulties could, however, be greatly eliminated, if not removed, with relatively small changes in design.The whole machine could be enclosed in a plastic bubble which would provide some protection in case of accidents.It would be easy to add a small petrol or electric motor.A wide variety of designs would be possible.As in rowing, we might employ the power of the arms or the general body musculature, as well as those of the legs; more muscular exercise would be good for the health of many people in cities, and a wide use of bicycle like muscle-powered vehicles would be a useful way to ensure this.It could also provide ample opportunities for showing off by the young and vigorous.
Enclosing the bicycle in a plastic bubble would _____.

A.make it easier to use

B.save muscular energy

C.provide protection from the weather

D.prevent it from colliding with other vehicles