Which command signifies a Marine is to stand at ease but still retains their position?

The command that signifies a Marine is to stand at ease while still retaining their position is "At Ease." This command allows Marines to relax in a manner that is more comfortable than standing at attention, yet they must remain in their place and maintain an awareness of their surroundings. They are allowed to move their arms and speak quietly with others around them, but they must still be ready to respond to further commands without delay.

The other commands have distinct meanings: "Fall In" directs Marines to form up in a specific formation, "Rest" allows for a more relaxed posture while still at attention, which may permit the Marines to move more freely but still requires some level of readiness, and "Dismissed" allows Marines to leave their formation and is a complete release from the standing command. Thus, "At Ease" is uniquely focused on relaxation within a defined stance, making it the correct choice.