Explanation:
Option A: Agent is the mediator who is responsible for answering all questions in the application.
Option B: The clients are not the person who can be taken into account for answering all the question. The client acts according to the agent
Option C: The owner does not have a role to answer question. So he cannot be taken into consideration. This option stands invalid.
Option D: None of these is invalid. Somebody has to be responsible for the said scenario.
