(Hitting set) Given a collection C = (S1, S2,..., Sn) of sub- sets of U let HCU be called a hitting set if HS; is non-empty for each Si, 1 i n. Show that the problem of deciding whether C has a hitting set of given size k is NP-Complete. You may assume that SAT, 3CNFSAT, k-Clique, k-Vertex Cover, k-IND, HAMILTONCYCLE are NP-Complete.