There are some good ideas to reduce the use of private cars. In 1989, for example, the authorities in Rome began an interesting experiment: passengers on the city buses did not have to pay for their tickets.
In Stockholm there was another experiment: people paid very little for a season ticket to travel on any bus, trolley bus, train or tram in all the city.
In many cities now some streets are closed to vehicles, and pedestrians are safe there.
In London there is another experiment: part of the street is for buses only, so the buses can travel fast. There are no cars or taxies in front of them.
What the writer worries about in a big city is ______.
A.the number of traffic lights
B.the shortage of buses
C.the lack of motorways
D.the traffic congestion
A.appetite
B.smell
C.interest
D.power
A.the greatest
B.more greater
C.greatest
D.even greater
A.occasional
B.accidental
C.enormous
D.immediately