Classify the following adjusting entries as involving prepaid expenses (PE), unearned revenues (UR), accrued expenses (AE), or accrued revenues (AR).
a. To record revenue earned that was previously received as cash in advance.
b. To record annual depreciation expense.
c. To record wages expense incurred but not yet paid (nor recorded).
d. To record revenue earned but not yet billed (nor recorded).
e. To record expiration of prepaid insurance.