Final answer:
The immediate action required for an unresponsive person who is not breathing or only gasping is to start CPR immediately.
Step-by-step explanation:
For a person who is unresponsive and not breathing or only gasping, the immediate action needed is to start CPR immediately (Choice A). Cardiopulmonary resuscitation (CPR) involves manual chest compressions to maintain circulation and provide oxygen to the brain until medical help arrives. This emergency procedure is critical as irreversible damage and death of neurons can occur within minutes of loss of blood flow. In contrast, an epinephrine injection (Choice B) is mostly used for severe allergic reactions, checking for a pulse and waiting for medical help (Choice C) would be too passive in this critical situation, and placing the person in the recovery position (Choice D) is not appropriate for someone who is not breathing.