Answer: They explain the beginnings of Post and Kellogg breakfast cereals
Step-by-step explanation:
To underscore the importance of advertising, the authors showed the beginnings of Post as well as the Kellogg breakfast cereals.
The point was that, these companies grew because of advertising and now hired thousand of people. If therefore, they hadn't advertised, they would not have grown the way they did to be able to take care of their employees who through salaries, are able to take over care of their daily life.