阅读理解。 The common cold is the world's most widespread illness. The most widespread mistake of all is that colds are caused by cold weather. They are not. They are caused by viruses (病毒) passing on from person to person. You catch a cold by coming into contact, directly or indirectly, with someone who already has one. If cold weather causes colds, it would be reasonable to expect the Eskimos to suffer from them forever. But they do not. And in isolated Arctic regions explorers (探险者) have reported being free from colds until coming into contact again with the outside world by way of packages and mails dropped from airplanes. During the First World War soldiers who spent long periods in the trenches, cold and wet, showed no increased tendency to catch colds. In the Second World War prisoners at the notorious Auschwitz concentration camp, naked and starving, were extremely surprised to find that they seldom had colds. At the Common Cold Research Unit in England, volunteers took part in the experiments in which they gave themselves to the discomforts of being cold and wet for long stretches of time. After taking hot baths, they put on bathing suits, allowed themselves to be with cold water, and then stood about dripping wet in drafty rooms. Some wore wet socks all day while others exercised in the rain until close to exhaustion. Not one of the volunteers came down with a cold unless a cold virus was actually dropped in his nose. If, then, cold and wet have nothing to do with catching colds, why are they more frequent (often) in the winter? Despite the most painstaking research, no one has yet found the answer. One explanation offered by scientists is that people tend to stay together indoors more in cold weather than at other times, and this makes it easier for cold viruses to be passed on. No one has yet found a cure for colds. There are drugs and pain suppressors such as aspirin, but all they do is to relieve the symptoms (症状). 1. Are the common colds caused by cold? ______________________________________ 2. When may Arctic explorers catch colds? ______________________________________ 3. How many kinds of people does the writer mention when explaining his idea? ______________________________________ 4. Why are the colds more frequent in the winter? ______________________________________ 5. What is the key point of this passage? ______________________________________