Select the graph that is not regular.

Group of answer choices

A graph with four vertices: A$,$ B$,$ C$,$ and D$,$ with undirected edges: A to B$,$ C to D$.$

A graph with four vertices: A$,$ B$,$ C$,$ and D$,$ with undirected edges: A to C$,$ A to D$,$ B to C$,$ B to D$,$ C to D$.$

A graph with four vertices: A$,$ B$,$ C$,$ and D$.$ Each vertex has an undirected edge to every other vertex.

A graph with four vertices: A$,$ B$,$ C$,$ and D$,$ with undirected edges: A to B$,$ A to C$,$ B to D$,$ C to D$.$