Which of the following can be defined as THE unique attribute used as a unique identifier within a given table to
identify a tuple?

A.
primary key

B.
candidate key

C.
foreign key

D.
secondary 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: A foreign key is an attribute in one table that matches the primary key of another table and is used to crossreference tables.
D: 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.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, New York, 2013, pp. 1174, 1179-1180
Stewart, 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