Please apply graph theory concepts here and show full explanations, thanks!
We define an orientation of an undirected graph G = (V, E) to be a directed graph G' = (V, E' ) that has the same set of vertices V and whose set of directed edges E' is obtained by giving each of the edges in G a direction.
That is, for each edge uv in E we can put in E' either the directed edge uv or the directed edge vu, but not both.
Let G = (V, E) be an undirected graph with n ≥ 2 nodes and let a, b be any two nodes in V .
Prove that G has some orientation that is a DAG in which c is a source and d is a sink.