Quiz: Graph Representations in Code

You build an adjacency list for an undirected graph with $V$ vertices using vector<vector<int>> adj(V). When you add edge $(u, v)$, you push $v$ into adj[u] and $u$ into adj[v]. What is the total size across all inner vectors after adding $E$ edges?

1. A.$E$
2. B.$2E$
3. C.$V + E$
4. D.$V \times E$