Choice "A" is correct.  The use of audit confirmations for an entity's accounts receivables is a required GAAP procedure if the accounts receivable balances are deemed material to the balance sheet. Choice "b" is incorrect. While the age of the accounts receivable account may indicate the potential lack of collectability, it is not a reason for confirmations to be required under GAAP. Choice "c" is incorrect. Confirmations are not required for accounts receivables that are immaterial or small. Choice "d" is incorrect. All accounts receivable are subject to valuation estimates (the estimate of the allowance for uncollectible accounts). The need for an allowance is not a criteria used to assess whether accounts receivable confirmations are required.