Choice "A" is correct. The FASB Accounting Standards Codification is the single source of U.S. GAAP. U.S. public companies are required to follow U.S. GAAP.
Choice "b" is incorrect. The International Financial Reporting Standards cannot be used by a U.S. public company as a source of U.S. GAAP.
Choice "d" is incorrect. FASB Statements of Financial Accounting Standards are included in the FASB Accounting Standards Codification, which is the single source of U.S. GAAP.
Choice "c" is incorrect. The FASB Statements of Financial Accounting Concepts are not GAAP.
