Final answer:
The preferred method of transferring Command is face-to-face, as it enables direct communication and confirmation of understanding, important in emergency management scenarios.
Step-by-step explanation:
The preferred method of transferring Command is A. Face-to-face. This method is considered most effective because it allows for direct communication, confirmation of understanding, and immediate feedback. Transfer of command procedures are critical in emergency management, and face-to-face transfers ensure that important information is not lost or misunderstood as can happen with methods like over the radio (B) or through documents. Neither the IAP (Incident Action Plan) protocol (C) nor the NIMS (National Incident Management System) protocol (D) are methods of command transfer; instead, they are tools used within the command structure for planning and managing incidents.