Which of the following can be defined as a unique identifier in the table that unambiguously points to an
individual tuple or record in the table?

A.
primary key

B.
candidate key

C.
secondary key

D.
foreign key

Explanation:
The primary key is the attribute that is used to make each row or tuple in a table unique.
Incorrect Answers:
B: Candidate keys are a subset of attributes that from which the database developer can choose the primary
key to uniquely identify any tuple or record in a table.
C: Secondary keys are candidate keys that have not been chosen as the primary key. The primary key is the
attribute that is used to make each row or tuple in a table unique. Candidate keys are a subset of attributes that
from which the database developer can choose the primary key.
D: A foreign key is an attribute in one table that matches the primary key of another table and is used to crossreference tables.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, New York, 2013, pp. 1174, 1179-1180Stewart, James, Ed Tittel and Mike Chapple, CISSP: Certified Information Systems security Professional Study
Guide, 5th Edition, Wiley Publishing, Indianapolis, 2011, pp. 276, 312
http://databases.about.com/cs/specificproducts/g/candidate.htm
http://rdbms.opengrass.net/2_Database Design/2.1_TermsOfReference/2.1.2_Keys.html