Indicate which of the following errors, each considered individually, would cause the trial balance totals to be unequal:

a. A fee of $15,000 earned and due from a client was not debited to Accounts Receivable or credited to a revenue account, because the cash had not been received.
b. A receipt of $6,000 from an account receivable was journalized and posted as a debit of $6,000 to Cash and a credit of $6,000 to Fees Earned.
c. A payment of $1,200 to a creditor was posted as a debit of $1,200 to Accounts Payable and a debit of $1,200 to Cash.
d. A payment of $10,000 for equipment purchased was posted as a debit of $1,000 to Equipment and a credit of $1,000 to Cash.
e. Payment of a cash withdrawal of $10,000 was journalized and posted as a debit of $1,000 to Salary Expense and a credit of $10,000 to Cash.

Indicate which of the preceding errors would require a correcting entry.