Which of the following graphs are trees? Select all that apply. c b d O O a & f g d = b e d O O a a o f h : s Let G be a tree. Suppose G has vertices a, b,c,d, e, f with the following degrees: deg(a) = 2, deg(b) = 1, deg(c) = 2, deg(d) = 2, deg(e) = 2, deg(f) = 1. Form a possible edge set for G by selecting its elements below. O {a,b} O {b,c] O {c,e } O fa,c] O {b,d} O {c, f } O {b,e } O {d,e } O {a,d} Ofa,e} O {b, f] O {d, f} O {a, f} O { c, d'} O {e, f }