Text 4Television--that most pervasive and persuasive of modem technologies, marked by rapid change and growth--is moving into a new era, an era of extraordinary sophistication and versatility, which promises to reshape our lives and our world. It is an electronic revolution of sorts, made possibly by the marriage of television and computer technologies.The world "television", derived from its Greek (tele: distant) and Latin (vision: sight) roots, can literally be interpreted as sight from a distance. Very simply put, it works in this way: through a sophisticated system of electronics, television provides the capacity of converting an image (focused on a special photoconductive plate within a camera) into electronic impulses, which can be sent through a wire or cable. These impulse, when fed into a receiver (television set) , can then be electronically reconstituted into that same image.Television is more than just an electronic system, however. It is a means of expression as well as a vehicle for communication, and as such becomes a powerful tool for reaching other human beings.The field of television can be divided into two categories determined by its means of transmission. First there is broadcast television, which reaches the masses through broad -based airwave transmission of television signals. Second, there is nonbroadcast television, through which provides for the needs of individuals or specific interest groups through controlled transmission techniques.Traditionally, television has been a medium of the masses. We are-most familiar with broadcast television because it has been with us for about forty - seven years in a form similar to what exists today. During those years, it has been controlled, for the most part, by the broadcast networks, ABC, NBC and CBS, who have been the major purveyors of news, information, and entertainment. These giants of broadcasting have actually shaped not only television but our perception of it as well. We have come to look upon the picture tube as a source of entertainment, placing out role in this dynamic medium as the passive viewer. With what topic is the passage primarily concerned（）

A. Recent changes in modem technology.
B. The marriages of broadcasting giants.
C. The role of television in today' s society.
D. The content of broadcast television programs.