【单选题】

Stinking buses, their passengers pale and tired, jam the crowded streets.Drivers shout at one another and honk their horns. Smog smarts the eyes and chokes the senses. The scene isAthens at rush hour. The city of Plato and Pericles is in a sorry state of affairs, built without a plan, lacking even adequate sewerage facilities, hemmed in by mountains and the sea, its 135 square miles crammed with 3.7 million pepole.EvenAthens’ ruins are in ruin: sulfur dioxiode eats away at the marble of the Parthenon and other treasures on theAcropolis.As Greek PremierConstantine Karamanlis has said, "The only solution forAthens would be to demolish half of it and start all over again."

So great has been the population flow toward the city that entire hinterland villages stand vacant or nearly so.About 120000 people from outlying provinces move toAthens every year, with the result that 40% of Greece’s citizenry are now packed into the capital. The migrants come for the few available jobs, which are usually no better than the ones they fleD、At the current rate of migration,Athens by the year 2000 will have a population of 6.5 million, more than half the nation.
Aside from overcrowding and poor public transport, the biggest problems confrontingAthenians are noise and pollution.
A、government study concluded thatAthens was the noisiest city in the worlD、Smog is almost at killing levels: 180 300 mg of sulfur dioxide per cubic meter of air, or up to four times the level that the World Health Organization considers safe. Nearly half the pollution comes from cars.Despite high prices for vehicles and fuel (＄2.95 per gallon) ,nearly 100000 automobiles are sold in Greece each year;3000 driver’s licenses are issued inAthens monthly.
After decades of neglect,Athens is at last getting some attention. In March a committee of representatives from all major public service ministries met to discuss a plan to unclog the city, make it livable and clean up its environment.
A、save-Athens ministry, which will soon begin functioning, will propose heavy taxes to discourage in-migration, a minimum of ＄5 billion in public spending forAthens alone, and other projects for the countryside to encourage residents to stay out.
A、master plan that will move many goverment offices to the city’s fringes is already in the works. Meanwhile, more Greeks keep moving intoAthens. With few parks and precious few oxygen-producing plants, the city and its citizens are literally suffocating.
According to the passage, one of the biggest problems confrontingAthenians is noise, which is mainly caused by ______.
A、buildings being demolished
B．highways being repaired
C．music being played
D．car horns being used