Which agency is responsible for investigating unfair or deceptive acts affecting commerce?

The Federal Trade Commission (FTC) is the agency tasked with investigating unfair or deceptive acts that affect commerce. Its primary role is to protect consumers and ensure a competitive marketplace by enforcing laws against deceptive business practices, such as false advertising and unfair competition. The FTC monitors and addresses issues across various industries, promoting transparency and fairness to ensure that consumers can make informed decisions. Additionally, the agency plays a significant role in antitrust law, which helps prevent monopolies and promotes healthy competition among businesses. This comprehensive focus on economic fairness and consumer protection establishes the FTC as the correct answer for this question.