听力原文： With the introduction of radio, newspaper publishers wondered how broadcasting would affect them. Many feared that radio, as a quick and easy means of keeping people informed, would displace the newspaper industry altogether. Others hoped that the brief newscast heard on the air would stimulate listeners' interest in the story, so they buy the newspaper to get more information. This second idea turned out to be closer to the truth. Radio and print were not substitutes for each other, but actually supported each other. You see, the relationship between different media is not always one of displacement, but can be one of reinforcement. However, this is not always the ease. Take television and motion pictures for example, with the popularization of TV, the motion picture industry suffered greatly. Movie attendance dropped when audience members chose to stay at home and be entertained. Likewise, when a football game was shown on the air, the stands were often empty, because fans chose to watch the game at home. What is the main topic of this talk?