Final answer:
The most appropriate action is to apply 100% oxygen via a nonrebreathing mask, immobilize the spine, keep warm, and transport rapidly.
Step-by-step explanation:
In this scenario, the most appropriate action to take is option D: apply 100% oxygen via a nonrebreathing mask, immobilize his spine, keep him warm, and transport rapidly.
Applying 100% oxygen through a nonrebreathing mask is important as it helps deliver oxygen to the patient's lungs and increase the oxygenation of his blood. Immobilizing his spine is crucial in case there is any spinal injury, as moving him without proper immobilization could cause further damage. Keeping him warm is necessary to prevent hypothermia, as cold water can rapidly decrease body temperature. Finally, transporting rapidly is important to get the patient to a medical facility where he can receive further care and evaluation.