I do not understand this question? "A graph G = (V,E) is bipartite if its vertices can be partitioned into two subsets V =A ? B such that all edges connect only vertices between the two sets (no two edges in the same set are connected)." what's meaning of that?

12. 6 points A graph G-(V,E) is bipartite if its vertices can be partitioned into two subsets V- AU B such that all edges connect only vertices between the two sets (no two edges in the same set are connected) (a) Prove or disprove: If a graph G is bipartite, then G is a tree. (b) Prove or disprove: If a graph G is a tree, then it is bipartite. eri