Final answer:
A borrower should be notified about the availability of primary loan servicing by certified mail within 90 days of their direct loan account becoming past due.
Step-by-step explanation:
The correct answer to the question is A. 90 days. A borrower should be provided with notification of availability of primary loan servicing by certified mail 90 days after the direct loan account becomes past due. This notification is important to ensure borrowers are aware of who is handling their loan servicing, and the use of certified mail provides a record of the notification being sent and received. Regulations such as these are part of borrower's rights and lender's responsibilities to provide transparent and fair communication regarding loan servicing.