In a relational database system, a primary key is chosen from a set of:

A.
Candidate keys.

B.
Foreign keys.

C.
Secondary keys.

D.
Cryptographic keys.

Explanation:
The correct answer is candidate keys by definition. Answer Foreign keys is incorrect because a
foreign key in one table refers to a primary key in another. Answer Secondary keys is a made-up
distracter, and answer Cryptographic key refers to keys used in encipherment and decipherment.