A、A rail. B、An engine. C、A thing like an arm. D、A computer controller. A

Some pessimistic experts feel that the automobile is doomed. They see a day in the not-too-distant future when all autos will be abandoned and allowed to rust. Other authorities, however, think the auto is here to stay. They hold that the car will remain a leading means of urban travel in the future.
    The motorcar will definitely change significantly over the next 30 years. It should become smaller, safer, and more economical, and should not be powered by the gasoline engines. The car of the future should be far more pollution-free than present types.
    Regardless of its power source, the auto in the future will still be the main problem in urban traffic jam.
    One proposed solution to this problem is the automated freeway system.
    When the auto enters the freeway system, an arm-like thing will drop from the auto and make contact with a rail that is similar to those powering elevated and subway trains.(17)Once attached to the rail, the car will become electrically powered from the system, and control of the vehicle will pass to a central computer. The computer will then monitor all of the car’s movements.
    The driver will use a telephone to dial instructions about his destination into the system.
    The computer will calculate the best route, and reserve space for the car all the way to the correct exit from the free way. The driver will then be free to relax and wait for the buzzer that will warn him of his coming exit.