Select the most correct answer
a. An index is a data structure used to speed access to tuples of a relation, given values of one or more attributes
b. The key for index can be any attribute or set of attributes, and need not be the key of the relation
c. We can think of the index as a binary search tree of (key, locations) pairs in which a key a is associated with a set of locations of the tuples
d. All of the others.
Answer: D