In the HITTING-SET problem, we are given a set U of items, and a collection of subsets of U, S1, S2,...,Sm. The problem is to find a smallest subset T of U such that T “hits” every subset Si, that is, T ∩ Si     = ∅, for i = 1,...,m. Design a polynomial-time O(log n)-approximation algorithm for HITTING-SET.