Classify the following adjusting entries as involving prepaid expenses, unearned revenues, accrued expenses, or accrued revenues.

$\backslash$table$[[$a$.$ To record services performed but not yet billed or recorded,Unearned revenues$],[$b$.$ To record annual depreciation expense,Prepaid expenses$],[$c$.$ To record expiration of prepaid rent,Prepaid expenses$],[$d$.$ To record cash received from a customer for services not yet provided,Prepaid expenses$],[$e$.$ To record office salaries expense incurred but not yet paid,Accrued expenses$]]$