Which of the following errors would cause the adjusted trial balance to be unequal ?

a. The adjustment for depreciation of $3,545 was journalized as a debit to Depreciation Expense for $3,454 and a credit to Accumulated Depreciation of $3,545.

b. The adjustment for prepaid insurance was omitted.

c. The adjustment for accrued fees of $16,340 was journalized as a debit to Accounts Payable for $16,340 and a credit to Fees Earned of $16,340.

d. The adjustment for unearned revenue was omitted.