Under what circumstance can a unit be suspended from requesting or receiving ammunition?

The correct choice states that a unit can be suspended from requesting or receiving ammunition when it combines unexpended ammunition with residue. This is crucial because combining these two types of ammunition can lead to safety hazards and impede accurate accountability and inventory management. Proper segregation of unexpended ammunition ensures that high standards of safety and compliance are maintained within the unit.

Additionally, unexpended ammunition and residue must be reported and handled correctly to prevent confusion regarding inventory and usage. This management is vital for compliance with regulatory guidelines, and any failure to adhere could jeopardize a unit's ability to responsibly manage its ammunition supply.

The other circumstances presented in the options, while potentially serious issues, do not specifically indicate an immediate suspension from requesting or receiving ammunition. They relate more to operational readiness and compliance but do not focus as directly on the safety and regulatory aspects tied to the handling of ammunition as the correct choice does. Therefore, the emphasis on the risks associated with mixing unexpended ammunition and residue makes it the most pertinent reason for a suspension.