Answer: C)paying affiliates to broadcast its programs
Explanation: CBS (Columbia Broadcasting System) is the broadcasting television system which is of the United States , similarly NBC( National Broadcasting Company) is also a radio network which overlooked the American television.
The competition between NBC and CBS was based on the terms of paying the official associates so that they can broadcast the programs of their television network.
Other options incorrect because they did not became competitors by charging low, broadcasting quiz and other shows,being obedient broadcasting network and on the basis of billboard advertisement .Thus, the correct option is option(c).