Quiz: Cycle Detection with Kahn's

You run Kahn's algorithm on a directed graph with $8$ nodes. The algorithm terminates with only $6$ nodes in the result. What happened?

1. A.Two nodes have no outgoing edges
2. B.The graph has a cycle involving the $2$ missing nodes
3. C.The algorithm found $2$ duplicate nodes and removed them
4. D.Two nodes are unreachable from any source