A candidate key is an attribute (or combination of attributes) that uniquely identifies each individual entity instance in a database. I am designing a database of historical houses in North Carolina that are still in existence at their original location. Which of the following attribute or attribute combinations could be a candidate key?

• A. The ZIP code portion of the house's address.
• B. The year the house was built.
• C. The name of the original owner of the house.
• D. None of the above; you'd need to generate a "HouseID" number.