The Sarbanes-Oxley Act mandates that the audit committee of the board of directors of public companies be directly responsible for the appointment, compensations, and oversight of the external auditors. In addition, the audit committee must preapprove all non-audit services that might be performed by the auditing firm.

Required
a. Discuss the rationale for this mandate as opposed to letting the shareholders, CFO, or CEO have these responsibilities.
b. What factors should the audit committee consider in evaluating the independence of the external auditor?