In terms of B(R), T(R), V (R ,x), and V (R ,y), express the following conditions about the cost of implementing a selection on R:

a) It is better to use index-scan with a non clustering index on x and a term that equates a; to a constant than a non clustering index on y and a term that equates y to a constant.

b) It is better to use index-scan with a non clustering index on x and a term that equates a; to a constant than a clustering index on y and a term that equates y to a constant.

c) It is better to use index-scan with a non clustering index on x and a term that equates x to a constant than a clustering index on y and a term of the form y > C for some constant C.