Which of the following is a true statement regarding audit evidence and audit procedures?

a. Inquiry is a type of audit procedure that typically does not require corroborating evidence.

b. The audit procedures that are performed during an audit are summarized in a document referred to as an audit engagement letter.

c. Reperformance involves checking the mathematical accuracy of a document or record, such as an inventory count sheet.

d. The auditor has a responsibility to design and perform audit procedures to obtain sufficient appropriate audit evidence.