When an auditor does not receive replies to positive requests for year-end accounts receivable confirmations, the auditor most likely would

a. Inspect the allowance account to verify whether the accounts were subsequently written off.

b. Increase the assessed level of detection risk for the valuation and completeness assertions.

c. Ask the client to contact the customers to request that the confirmations be returned.

d. Increase the assessed level of inherent risk for the revenue cycle.