How this should be done?

It was mentioned in class that a graph (undirected with no loops) is bipartite if and only if it does not contain a cycle of odd length. This characterisation of bipartite graphs was used to show that the class of all bipartite graphs is axiomatizable. (a) Dene a theory S in the signature 0g, := (E) of graphs such that for any graph G, G is nonbipartite if and only if there is a sentence (p E S such that G|=go. (b) Use Question 5 to deduce that the class of all nonbipartite graphs is not axiomatizable