In $O(|V|+|E|)$, we can detect whether a Directed Graph has a cycle or not. ---> True
In depth-first seach on DAG, there is no Back Edge. ---> True
With known Number of Edges, in $O(|V|)$ and not $O(|V|+|E|)$, we can detect whether a simple undirected Graph has a cycle or not. ---> True
Am I right about the above three questions about Graph Algorithm? I think all of them is True?