Self Doubt (Graphs)

Question

How to understand this: For a connected graph, V = O(E))

SOURCE http://www.geeksforgeeks.org/greedy-algorithms-set-5-prims-mst-for-adjacency-list-representation/

prims algorithm time complexity for adjacency list representation. Also same is given in CLRS but no reason 

Comments

It means that the in a connected graph the no. of vertices can never exceed the no. of edges because minimum edges in a connected graph of $n$ nodes will be $O(n)$ and maximum no of edges will be $O(n^2)$

---

Thanks but can you share some resources to understand it better.