Choice "C" is correct. If the omitted audit procedures impair the auditor's ability to support the previously issued opinion, the auditor should promptly undertake to apply the omitted procedures (or alternative procedures).
Choice "a" is incorrect. The auditor's specific approach to identified risks at the relevant assertion level is not relevant in evaluating whether an omitted audit procedure should be applied. This determination should be based on whether the omission of the procedure impairs the auditor's ability to support the opinion.
Choice "d" is incorrect. Whether or not the working papers are subject to postissuance review in connection with a peer review program is not relevant in evaluating whether an omitted audit procedure should be applied. Sufficient evidence to support the opinion is necessary regardless of whether or not there will be a peer review.
Choice "b" is incorrect. If the results of other procedures that were applied tended to compensate for the one omitted, there would be adequate support for the audit opinion, and the omitted procedure would not need to be applied.