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.