A common courtesy when an officer enters the office or classroom for the first time of the day is to...

When an officer enters the office or classroom for the first time of the day, a common courtesy is to call the room to attention. This action demonstrates respect and acknowledgment of the officer’s presence. It signifies an understanding of military protocol and instills discipline within the environment. Calling the room to attention serves as a reminder of order and hierarchy, fostering a sense of unity among the cadets as they collectively show respect for the officer.

Remaining seated until instructed or standing up and saluting are specific actions that may be appropriate in different contexts but do not encapsulate the initial response upon the officer's entrance. Introducing the officer to everyone present could be a courteous action but is typically not the primary expectation that aligns with established military customs in this scenario. Thus, calling the room to attention is the action that best embodies the expected response to properly honor an officer arriving for the first time that day.