Which of the following sets of edges represent subgraphs of the graph that are trees? (Select all that apply.)

{{a, d}, {c, d}, {d, e}, {d, f}}

{{a, b}, {a, c}, {a, f}, {b, c}, {d, e}}

{{a, f}, {b, f}, {c, f}, {d, e}, {d, f}}

{{b, f} {c, f}, {d, e}}