Sally is the mortgagor. Most people confuse mortgagor and mortgagee; in this case the mortgagee is the bank. The question plainly states that Mary bought Sally's property, which was subject to a mortgage. It does not state that there was any loan assumption. Thus, Sally remains totally liable on the loan and cannot sue Mary. The bank, which is the mortgagee, can sue only Sally, as there was no assumption.