Final answer:
Among the listed examples, monopolistic competition is not considered an antitrust activity; whereas price fixing, market allocation, and mergers and acquisitions can be, if they harm competition.
Step-by-step explanation:
Examples of antitrust activities include a range of actions that are intended to promote fair competition in the marketplace and prevent monopolistic behavior. Among the list provided, price fixing, market allocation, and mergers and acquisitions are indeed activities that could potentially violate antitrust laws if they reduce competition and harm consumers. However, monopolistic competition is a market structure in which many companies sell products that are similar but not identical and is generally not considered an antitrust activity, as firms in monopolistic competition do not have the market power to dictate prices or engage in anticompetitive practices on their own.