An ________ on an attribute of a relation is a data structure that allows the database system to find those tuples in the relation that have a specified value for that attribute efficiently, without scanning through all the tuples of the relation.

An ________ on an attribute of a relation is a data structure that all

1.	An ________ on an attribute of a relation is a data structure that allows the database system to find those tuples in the relation that have a specified value for that attribute efficiently, without scanning through all the tuples of the relation.
A.	Index
B.	Reference
C.	Assertion
D.	Timestamp
Answer» B. Reference