Which command must be acknowledged with a response before entering a room?

The most appropriate command that must be acknowledged with a response before entering a room is "Coming In." This command serves as a clear warning to those inside the room that someone is about to enter. It is primarily used to prevent accidental confrontations or tactical surprises, ensuring that anyone inside has a chance to respond appropriately. By requiring an acknowledgment, this command enhances communication and situational awareness among team members, contributing to overall safety and effectiveness during operations.

In contrast, while commands like "All Clear" and "Support" play vital roles in team operations, they do not specifically indicate an imminent entry into a space. "Last Man Set" is typically used to signify that the last member of a team is positioned and ready to proceed, but it also does not pertain directly to the act of entering a room and does not require a response to maintain safety protocols during entry.