Given that x = {1,2,3,4}, list the elements of each of the following sets: (a) {A:A ⊆ x and |A| = 2} (b) {A:A ⊆ x and |A| = 1} (c) {A:A is a proper subset of x} (d) {A:A ⊆ x and 1 ∈ A