Hosts Can Often Be Attacked in Layers

Multiple Choice

Hosts can often be attacked in layers. If the target service is not vulnerable then what else should the attacker try? (Choose two)

A) Annoy the administrator of that host with a Denial of Service attack
B) If the target service is secure there is nothing else that can be done
C) Convince a user to accept a malicious file into one of the clients on the host
D) Attack a service on one of the other open ports