Final answer:
For a person with a suspected head or neck injury, the airway should be opened by keeping their head and neck in a neutral position and providing first aid without moving them, while calling for emergency assistance.
Step-by-step explanation:
If you suspect a person has a head or neck injury, option 3, keeping the person's head and neck in a neutral position, is the correct way to open their airway. It is crucial not to move them, as permanent paralysis and other serious complications may result from improper handling. Instead, provide basic first aid, which includes stopping any bleeding and making the person comfortable without moving the head or neck. Additionally, call for emergency medical assistance immediately and keep the person very still.