Please answer the following question: I'm taking a test and have to guess the right answer to the question after the article. Article: The world itself is becoming much smaller by using modern traffic and modern communication means . Life today is much easier than it was hundreds of years ago, but it has brought new problems. One of the biggest is pollution. To pollute means to make things dirty. Pollution comes in many ways. We see it, smell it, drink it and even hear it. Man has been polluting the earth. The more people, the more pollution. Many years ago, the problem was not so serious because there were not so many people. When the land was used up or the river was dirty in a place, men moved to another place. But this is no longer true. Man is now slowly polluting the whole world. Air pollution is still the most serious. It's bad to all living things in the world, but it is not only one kind of pollution. Water pollution kills fish and pollutes drinking water. Noise pollution makes us become angry more easily. Many countries are making rules to fight against pollution. They stop the people from burning coal in houses and factories in the city, and from blowing dirty smoke into the air. The pollution of SO2 is now the most dangerous problem of air pollution. It is mostly caused by heavy traffic. It is certain that if there are fewer people driving, there will be less air pollution. The earth is our home. We must take care of it. That means keeping the land, water and air clean. And we must try to control the growth of population at the same time. Question: What is the most dangerous problem of air pollution? Options: A: CO2 B: H2O C: SO2 D: CO
A:
C