Final answer:
If an auditor of a public company cannot find guidance issued by the PCAOB, they should seek guidance from the Securities and Exchange Commission (SEC).
Step-by-step explanation:
If an auditor of a public company cannot find guidance issued by the PCAOB on a particular audit matter, the auditor should generally seek guidance from Regulations issued by the Securities and Exchange Commission. The PCAOB (Public Company Accounting Oversight Board) is responsible for establishing auditing and related professional practice standards for public company audits. However, if the guidance is not found from the PCAOB, the Securities and Exchange Commission (SEC) is the regulatory agency that oversees the securities industry and can provide additional guidance. Therefore, option C) Regulations issued by the Securities and Exchange Commission would be the most relevant source of guidance in this scenario.