Which of the following statements regarding allowance for doubtful accounts is true? A. Under the aging of accounts receivable method, bad debt expense is calculated and then added to the beginning balance in the allowance for doubtful accounts. B. The allowance for doubtful accounts is a contra-revenue account. C. The allowance for doubtful accounts is credited when a specific write-off is recorded. D. The allowance for doubtful accounts has a normal credit balance.