Complex sentence: The U.S. Securities and Exchange Commission (SEC) is a federal agency which holds primary responsibility for enforcing the federal securities laws and regulating the securities industry, the nation's stock and options exchanges, and other electronic securities markets in the United States.
Split into simpler sentences: The U.S. Securities and Exchange Commission (SEC) is a federal agency. It holds primary responsibility for enforcing the federal securities laws and regulating the securities industry, the nation's stock and options exchanges, and other electronic securities markets in the United States.