Which of the following methods of determining bad debt expense does not properly match expense against revenue?
a) Charging bad debts with a percentage of sales under the allowance method.
b) Charging bad debts with a percentage of accounts receivable under the allowance method.
c) Charging bad debts with an amount derived from aging accounts receivable under the allowance method.
d) Charging bad debts as accounts are written off as uncollectible.