Final answer:
In the United States, where five companies control 90% of media outlets, this situation is known as an b) oligopoly.
Step-by-step explanation:
Today in the United States, the scenario where just five companies control 90 percent of media outlets is an example of an oligopoly. An oligopoly is a market form in which an industry or sector is dominated by a small number of firms. In contrast, a monopoly exists when only one firm controls an entire industry.
The significant concentration of media ownership within a few large corporations has various implications, which can include a lack of competition, innovation, and diversity in viewpoints and information shared with the public.