单选题 The most widespread fallacy (谬误) of all is that colds are caused by cold. They are not. They are caused by viruses passage on from person to person. You catch a cold by coming into contact, directly or indirectly, with someone who already has one. If cold causes colds, it would be reasonable to expect the Eskimos to suffer from them permanently. But they do not. And in isolated arctic regions explorers have the outside world by way of packages and mail dropped from airplanes.
Arctic explorers may catch colds when

• A. they are working in the isolated arctic regions.
• B. they are writing reports in terribly cold weather.
• C. they are free from work in the isolated arctic regions.
• D. they are coming into contact with the outside worl