What is the first thing CC should do if N1 calls to the flight deck?

When N1 calls to the flight deck, it is critical for the cabin crew to prioritize safety and assess the situation immediately. Stopping all boarding activities is essential because it helps to maintain control and manage any potential emergencies effectively. It ensures that no additional passengers are boarding who could complicate the situation, provides a clear area for emergency personnel if required, and allows the crew to respond to the situation without any distractions or additional stressors from boarding passengers.

In emergencies, securing the cabin environment is paramount, which is why halting boarding is a standard procedure. This step allows the crew to verify the current passenger list, ensure everyone is accounted for, and focus on the issues at hand without added chaos. By taking this action first, the cabin crew can create a safer environment for both passengers and staff.

The other options, while important in their own right, do not address the immediate need for safety and order as effectively as halting boarding does.