What must be done to the combination of security containers that store classified material?

The correct answer emphasizes the importance of ensuring that security containers, which store classified material, are protected at the highest classification level. This is critical because classified materials are sensitive and contain information that, if disclosed, could harm national security or compromise safety. By protecting these containers at the highest level, organizations ensure that only authorized personnel have access to the information, thereby mitigating risks related to espionage, unauthorized access, and potential leaks.

Additionally, securing these containers appropriately helps maintain compliance with government regulations and security protocols designed to safeguard classified information. Such measures are fundamental in maintaining the integrity of sensitive data and protecting the interests of national security.

The other options do not adhere to the established protocols regarding classified information; sharing combinations, documenting them casually, or writing them on the containers could lead to unauthorized access and breach of security measures.