Final answer:
A deed of trust is the security instrument involving three parties: the borrower, the lender, and the trustee. It is distinct from a mortgage, promissory note, or lease agreement, which generally involve fewer parties.
Step-by-step explanation:
The security instrument that involves three parties is a. Deed of trust. In a deed of trust, the three parties involved are the borrower (trustor), the lender (beneficiary), and the trustee. The trustee holds legal title to the property as security for the repayment of the debt and will carry out the process of foreclosure if the borrower defaults on the loan. This is different from a typical mortgage, which typically involves only two parties, the borrower and the lender. A promissory note is a written promise to pay a specified sum of money to a specified person or the bearer at a specified date or on demand, while a lease agreement is a contract outlining the terms under which one party agrees to rent property owned by another party.