For many years, Carefree Company has estimated Bad Debt Expense using the aging of accounts receivable method. Assuming Carefree has no write-offs or recoveries, its estimate of uncollectible receivables resulting from the aging analysis equals

a. Bad Debt Expense for the current period.
b. The ending balance in the Allowance for Doubtful Accounts for the period.
c. The change in the Allowance for Doubtful Accounts for the period.
d. Both (a) and (c).