Which of the following is NOT a rest position that can be given at a halt?

The correct answer is based on the understanding of military drill commands. "Stand at attention" is not a rest position; rather, it is a command that signifies a soldier should remain in a rigid, alert stance. In this position, the individual is expected to maintain a high level of focus and readiness.

In contrast, the positions of "At ease," "Parade rest," and "Rest" are all defined as rest positions that allow personnel to relax their posture while remaining responsible for their surroundings. "At ease" permits a relaxed stance while remaining silent, "Parade rest" involves standing with feet apart and hands clasped behind the back, and "Rest" allows for a more relaxed state, often with hands resting on the hips. Thus, "Stand at attention" is the only option listed that does not allow for any relaxation in posture, making it the correct choice for the question.