Final answer:
The appropriate flag to be flown when the commanding officer is on leave is the Ensign flag.
Step-by-step explanation:
When your commanding officer is on leave, the appropriate flag to be flown is the B. Ensign.
The Ensign flag is used to indicate that the commanding officer is absent and the ship is under the command of the executive officer or second in command. It is a signal to other vessels and is flown from the stern of the ship.
During the commanding officer's absence, the executive officer assumes temporary command and the Ensign flag is used to communicate this change in leadership.