Final answer:
The Sarbanes-Oxley Act established the Public Company Accounting Oversight Board (PCAOB) to regulate auditing practices of public companies. The PCAOB is responsible for auditing, establishing standards, and enforcing compliance, but it does not regulate private companies.
Step-by-step explanation:
The Sarbanes-Oxley Act, enacted in 2002, established the Public Company Accounting Oversight Board (PCAOB) to regulate and oversee the auditing practices of public companies. The PCAOB is responsible for auditing public companies, establishing auditing standards, and enforcing compliance with those standards. However, the PCAOB does not have the authority to regulate private companies. So the correct answer is 4) Regulating private companies.