When classified information is removed from storage during working hours, how must it be protected when not in use?

When classified information is removed from storage during working hours, it is critical to maintain its security until it is no longer needed. The correct choice indicates that classified documents should be kept face down under constant surveillance. Keeping documents face down can help prevent unauthorized individuals from inadvertently viewing sensitive information. The requirement for constant surveillance ensures that someone is always monitoring the documents to protect against unauthorized access or breaches.

Maintaining both the visibility management and the continuous observation makes it an effective measure to mitigate risk. This practice aligns with the principles of protecting classified information, ensuring that even when documents are in use, they do not become too accessible or visible to those who do not have the necessary clearance, thereby preserving the integrity of the information.