Final answer:
The media serves as an agenda-setter by influencing public attention, a gatekeeper by deciding what stories to cover, and a watchdog by exposing wrongdoing.
Step-by-step explanation:
Media as agenda-setter: The media begins reporting about a disgusting-looking ingredient found in many common foods, which leads to a major movement to outlaw the ingredient.
Media as a gatekeeper: The evening news runs a story about the mayor's plan to build a new park instead of covering a protest against cutting bus transportation.
Media as watchdog: Two television networks run exposés about a politician's bad behavior, prompting the politician to return the gifts and resign from office.