A、How much a TV set costs. B、The quality of TV programs. C、How people put it to use. D、The number of people watching TV. C文章最后说：

Television now plays such an important part in so many people’s lives that it is essential for us to try to decide whether it is a blessing or a curse. Obviously television has both advantages and disadvantages. But do the former outweigh the latter? In the first place, television is not only a convenient source of entertainment, but also a comparatively cheap one. They just sit comfortably at home and enjoy endless series of programs rather than to go out in search of amusement elsewhere. Some people, however, maintain that this is precisely where the danger lies. The television viewer needs to do nothing. He is completely passive and has everything presented to him without any effort on his part Secondly, television keeps one informed about current events, allows one to follow the latest developments in science and politics. Yet here again there is a danger. The television screen itself has a terrible, almost physical fascination for us. We get so used to looking at its movements, so dependent on its pictures that it begins to dominate our lives. There are many other arguments for and against television. The poor quality of its program is often criticized. But it is undoubtedly a great comfort to many lonely elderly people. And does it corrupt or instruct our children? I think we must realize that television in itself is neither good nor bad. It is the uses to which it is put that determine its value to society.
16. What is NOT mentioned as the disadvantages of TV?
17. What is the speaker’s opinion of television?
18. What determines the value of television to society?