Unless there are specific choices I can only offer you a list of potential answers.
Sherman Act (1890), Federal Trade Commission Act (1914), and the Clayton Act (1914).
The Sherman Act outlawed all forms of monopolization and any attempts to do so. It also set strict penalties for any and all violations of this law.
The Federal Trade Commission Act of 1914 created the Federal Trade Commission which oversaw national business practices.
The Clayton Act addresses more specific points but especially focuses on preventing monopolies through regulation of mergers and acquisitions. It also goes on to prevent discriminatory pricing and dealings.
Further reading can be found on: https://www.ftc.gov/tips-advice/competition-guidance/guide-antitrust-laws/antitrust-laws
