Choice "A" is correct. The ethical standards that apply to the audits of issuers (SOX/PCAOB/SEC) require that the lead partner rotate off the audit engagement after 5 years. The AICPA Code of Professional Conduct, which is followed when auditing nonissuers, does not require audit partner rotation.
Choice "b" is incorrect. All U.S. ethical standards prohibit the performance of financial information systems design and implementation services for audit clients.
Choice "d" is incorrect. Loans to or from clients, other than loans from financial institutions under normal lending policies, are prohibited for audits of issuers and nonissuers under all ethical standards.
Choice "c" is incorrect. Any direct financial interest in a client impairs independence, whether the client is an issuer or a nonissuer.