Which of the following is not acceptable in estimating uncollectible accounts receivable under GAAP?
a. The estimate of uncollectible accounts is based on a percentage of sales for the period.
b. The estimate of uncollectible accounts is based on a percentage of the accounts receivable balance at the end of a period.
c. The estimate of uncollectible accounts is based on an aging schedule.
d. No estimate of uncollectible accounts is made; accounts are written off when it is determined they cannot be collected.