听力原文： Originally just a novelty, television has become the most important entertainment medium in American culture. Although TV was invented in the 1920s, it didn't enter popular culture until 1948, following a short period serving elite culture. By the 1960s it was playing a major role in reflecting and shaping culture. Television entertainment has changed during the past 40 years to reflect an ever-changing culture. Sitcoms, talk shows and made-for-TV movies are now dealing with controversial and socially relevant topics. One of the latest trends has been the change in image from the 'nuclear family' to nontraditional family sitcoms. Television news was primitive in the development days, but it soon became a powerful force. Eventually it dominated the news scene, with more people reporting that they got their news from TV than from any other source. In the 1960s, when assassinations and riots received major coverage, people started blaming TV for shaping the news. Local television news began changing in the 1970s to become more entertaining for the masses. Feature stories and humor were added to the evening newscast, and newscasters began to be hired for their looks and personalities rather than their news judgment. Networks, which have been a major source of news and information since the early days of television, found that new technologies, such as satellites, were making local news shows more competitive by the 1990s. Television's impact on our culture has been staggering. Ninety-eight percent of American homes have at least one TV set. TV has become one of the most powerful socializing agents in our culture. Children spend more hours watching TV than they spend in school. The average American home has the TV set on more than seven hours a day. Despite the widespread acceptance of television into our culture, it remains a controversial enterprise. Violence on TV has been a concern since the beginning, with many people citing the information-imitation theory to support their argument. Another concern about television's effect on children developed more recently: in the 1980s toy manufacturers started producing product-oriented cartoons for children. By the mid- 1980s these 30-minute commercials dominated children's television. Television's impact on the learning environment of children has been a concern since the early 1950s. Research has shown that TV does influence children but that the degree of that influence seems to depend on the level of involvement of the parents and the quality of the child's home life. Given the changes in the nuclear family and the growing number of 'latchkey kids,' there is new concern about TV's influence. By the 1980s television had entered a fragmented stage. Public broadcasting was providing noncommercial programming for the high or elite culture, while cable and satellite channels offered a large variety of specialized programs to meet particular interests. And perhaps inevitably, television, which had from the beginning been a vehicle to deliver large audiences to advertisers, now offered teleshopping channels that ran nothing but ads 24 hours a day. Business trends in television have built this relatively new mass communication medium into the second largest generator of advertising revenue with more than ＄27 billion spent each year on commercials. (56)