When Airmen are armed with the M9, where must they keep it?

The correct choice emphasizes the importance of firearm safety and proper handling protocols for the M9 service pistol. Airmen must keep the weapon holstered at all times except during specific situations, such as when they are engaged in their line of duty or when clearing the weapon for turn-in.

This requirement serves multiple purposes: it minimizes the risk of accidental discharge, ensures the weapon is securely stored while not in use, and maintains a controlled environment for firearm handling. By only removing the weapon from its holster during these defined circumstances, it reinforces safety measures and accountability.

The other choices do not align with established protocols for firearm handling. Keeping the weapon on the hip at all times could lead to unsafe situations if not managed correctly. Holding the firearm while at attention is impractical and unsafe, and placing it on a gun rack is not compliant with the requirement for ensuring the weapon is holstered securely when not in use. Therefore, the given answer reflects a commitment to safety and adheres to standard operating procedures.