Let U = {-9, -5, -1, 1, 4, 6, 9, 13, 17, 18}, A = {-9, -1, 4, 9, 17}, B = {-5, 1, 6, 13, 18}, and C = {-9, -5, 1, 4, 13, 17}. List the elements of each set. (Enter your answers using roster notation. Enter {} or ∅ for the empty set.)