Which deck house is used while the ship is in port?

The designation of Deck House 3 as the correct answer stems from its specific function and purpose when the ship is in port. Deck House 3 typically serves as the primary area for conducting administrative and operational duties, including various personnel functions, briefings, and watch standing. This location is usually equipped with the necessary communications and data resources that facilitate effective ship operations while in harbor.

While other deck houses may also have roles during at-sea operations or specific equipment management, Deck House 3 is designed and utilized primarily for activities that support the ship's personnel and command structure when the vessel is docked. It serves as a hub for sailors to manage daily tasks and coordinate with the shore-side support, making it the most fitting option when referring to the necessary operational space during port calls.