Consider a relation R (a, b, c, d) that has a clustering index on a and no clustering indexes on each of the other attributes. the relevant parameters are: B(R) = 1000, T(R) = 5000, V(R, a) = 20, V{R, b) = 1000, V(R, c) = 5000, and V(R, d) = 500. Give the best query plan (index-scan or table-scan followed by a filter step) and the disk-I/O cost for each of the following selections: Sigma_a = 1 AND 6 = 2 AND d = 3(R) Sigma_a =l AND b=2 AND c greaterthanorequalto 3(-R) Sigma_a= 1 AND b