Auditors commonly set inherent risk as high for valuation of accounts receivable. which of the following controls would help reduce the likelihood of un collectible accounts?

a. Credit approval by an employee independence of the sales function.

b. Preparation of a periodic aged accounts receivable trial balance for review and follow-up by appropriate management personnel.

c. A policy of writing off uncollectible accounts when they are no longer likely to be collected.

d. All of the above.