Allowance for Doubtful Accounts has a credit balance of $1,466 at the end of the year (before adjustment), and an analysis of customers' accounts indicates uncollectible receivables of $19,785. Which of the following entries records the proper adjustment for bad debt expense?

a. debit Bad Debt Expense, $21,251; credit Allowance for Doubtful Accounts, $21,251

b. debit Allowance for Doubtful Accounts, $21,251; credit Bad Debt Expense, $21,251

c. debit Bad Debt Expense, $18,319; credit Allowance for Doubtful Accounts, $18,319

d. debit Allowance for Doubtful Accounts, $18,319; credit Bad Debt Expense, $18,319