Explanation:

- Option 1: Mortgagor

- The mortgagor is the borrower in a mortgage.

- They retain possession of the property in a simple mortgage.

- They give the mortgagee a legal claim to the property as security for the loan.

- Option 2: Mortgagee

- The mortgagee is typically the lender or bank.

- They do not have possession of the property in a simple mortgage.

- Option 3: Co-owner

- A co-owner might own the property jointly but doesn’t relate specifically to a simple mortgage.

- Option 4: Administrator

- An administrator manages or oversees something, such as an estate, but isn’t directly related to simple mortgage possession.

Option 1: Mortgagor is the correct answer.