Which of the graphs above are bipartite? Give your answer as a sequence of the labels separated by some spaces in any order such as "b a". Don't use commas or parentheses.
Graph a is bipartite: The first color is assigned to the top-left, bottom-middle, and top-right vertices; the second color is assigned to the other three vertices.
Graphs b and c are not bipartite, as they contain cycles of odd length.