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

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

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

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

d. All of the above