Choice "B" is correct. Audit documentation serves mainly to provide: 1) the principal support for the auditor's report; 2) assistance in the planning, conduct, and supervision of the audit; 3) accountability; and 4) useful information.
Choice "d" is incorrect. Audit documentation does not satisfy the auditor's responsibilities concerning the Code of Professional Conduct.
Choice "a" is incorrect. Audit documentation does not monitor the effectiveness of the CPA firm's quality control activities.
Choice "c" is incorrect. Audit documentation does not document the level of independence maintained by the auditor.