Characteristics of Eulerian Graph/Sufficient Condition

Theorem
Let $G$ be a finite (undirected) graph which is connected

Let each vertex of $G$ be even.

Then $G$ is an Eulerian graph.

Note that the definition of graph here includes:
 * Simple graph
 * Loop-graph
 * Multigraph
 * Loop-multigraph

but does not include directed graph.