Which of the following statements best describes an auditor's responsibility to detect fraud?

a. The auditor is responsible for failing to detect fraud when the failure clearly results from not performing audit procedures described in the engagement letter.

b. The auditor must extend auditing procedures to search actively for fraud.

c. The auditor must assess the risk that material fraud may exist.

d. The auditor is responsible for failing to detect fraud only when an unqualified opinion is issued.

Choose the correct answer.