Answer: A. Lien theory
Explanation: Lien Theory simply refers to the concept whereby a property (most especially mortgage) serves as collateral for a loan. Here, the mortgage serves as the Lien on the property, and this is what the lender (mortgagee) acquires, while the borrower (mortgagor) retains the deed and rights of the property.
The lender (mortgagee) can start foreclosure procedure on the property if the borrower (mortgagor) defaults in the payment of the loan.
A state where this theory is practiced is called a Lien Theory State.