【正文】 mber 1, 1930, a dense fog moved over the Meuse Valley, in Belgium. Many factories in the valley poured smoke and fumes into the foggy air. This created a dark smog of smoke and fog bined. People in the valley began to cough and strain for breath. The smog remained for four days. During that time, thousands of people became ill. The hospitals were filled with patients. Sixty people died. Most of them were older persons with heart and lung problems. Finally, a heavy rain washed away the smog. Scientists studied the causes of the disaster. They concluded that the illnesses and deaths were caused by chemicals in the smog.The first reported event of this kind in the United States happened in Donora, a factory town in a valley near Pittsburgh. In 1948, a killer smog made half of the population sick, there were 17 deaths. Again, older people with lung or heart diseases were hit hardest.London, England, has always been known for its black fags. In the winter of 1952, a milky white fog rolled into the city. It soon turned into black smog as the smoke of the city poured into the air. It was so hard to see that people had to walk in front of the buses to guide them. In this way, the most serious air pollution disaster in history began. When it was over, more than 4,000 people had been killed by the thick black smog.New York City has had several Londontype smogs since 1950. Each time, there were from 100 to 400 deaths caused by the smog. Although these smogs were not as deadly as London’s, New York City has the worst: air pollution problem in the United States.In all the killer smogs, factories and homes poured smoke and fumes into the air from the furnaces. The chemical fumes bined witty the water droplets in the fog to form harmful substances. These substances caused the illness of those who breathed the polluted air.Usually, such harmful fumes rise into the upper air and are blown away by the wind. Hut sometimes there is an unusual weather condition called a temperature inversion. A layer of cold air remains near the ground as smoke and fumes pour into it. This is covered by an upper layer of warm air that acts like a lid. It prevents the polluted cooler air from rising. The harmful fumes pile up and make people ill. The smog may bc so thick that airports are closed and chains of collisions occur on the highways.Another type of smog occurs in Los Angeles. Here the weather may he clear and sunny. But stinging eyes and dry coughs show that harmful chemicals fill the air. The smog is due to invisible gases, mostly from automobile exhaust. Because these chemicals are changed by the sun high up in the air, Los Angeles smog is called photochemical smog. It contains automobile exhaust fumes and nitrogen oxides changed by the sun39。s rays. Added to these are sulfur dioxide and other fumes from factories and oil refineries. Photochemical smog is found in many large cities all over the world.Killer smogs don39。t happen very often, fortunately. Hut in many large cities, a bination of automobile exhaust fumes, home furnace smoke, and factory waste gases pours into the air. This may also happen in the suburbs, or out in the country, where large factories have been built. A number of harmful substances have been found in the air there. When these substances are breathed in day after day, the health of the population is affected.20A. You Can’t Do It Because It Hurts NobodyWho do you think breaks the law in our society? If you believe that only tough guys mit crimes, you may have to think again. Answer the following questions honestly, Has anyone you know ever driven drunk? Can you think of a friend who has used drugs? Are you aware that your parents may not always tell the truth when they go through customs? Won39。t some of your friends admit that they have stolen an item from a store? Have any of your friends ever copied a CD onto a tape for someone else?In case you did not know, all of these acts are against the law. Now, among the people you know, how many have never broken the law? Does that mean that most members of our society should go to jail? Unlike in the movies, we can’t divide the world into bad guys and model citizens. Real life is much more plex. In the same way that diseases range from the mon cold to fatal forms of cancer, crimes vary in degree. For example, smoking in an elevator will inconvenience people, but much less than threatening them with a gun.In addition to breaking the law themselves, people tolerate various levels of crime. Why are we tolerant of some crimes? It may be that, by seeing others do something, we accept it more easily. We may even start mitting that crime ourselves. For instance, most people will find it easier to speed on a highway when everybody else is driving over the speed limit. When people celebrate a sports championship, if they see someone breaking store windows, they might start breaking windows themselves or even steal from the store. So the people around us influence how much lawbreaking we can tolerate.We must also wonder whether seeing violence on television or reading about it in the newspapers every day makes us tolerate crime more than we should. We bee used to seeing blood on the news on television, or in full color in newspapers and magazines. Because we see thousands of dead people on TV, maybe we just try to ignore the situation behind the violence.If so many citizens tolerate violence and crime, or even mit crimes themselves, it may simply be because of the human mind. Our minds may not care about specific laws. Instead, our minds may have a system of values that usually prevents us from hurting other people to improve our own lives. Yet, when it es to respecting the rights of a mass of anonymous individuals, we might not be so responsible. While most people would not steal a wallet containing $50, they may not mind cheating on taxes, because cheating on taxes does not hurt any one person. It hurts society, but society