Answer:
c. not earned but the cash has been received
Explanation:
Deferred revenue refers to those payments which have been received in advance against which services are yet to be provided.
These constitute a liability since an enterprise still owes an obligation of providing services which are outstanding for which money has already been received.
As per accrual basis of accounting, deferred revenues are recognized as revenue only when the services pending against those have been provided. Till that point, such a revenue is regarded as a liability.
