Final answer:
b. Use the head tilt-chin lift. The best way to open the airway of an unresponsive victim with no suspected neck injury is to use the head tilt-chin lift technique.
Step-by-step explanation:
The best way to open the airway of an unresponsive victim with no suspected neck injury is to use the head tilt-chin lift technique. This technique involves placing one hand on the victim's forehead and gently tilting the head back while the other hand is used to lift the chin. By doing this, the airway is opened and any obstructions can be cleared.
Using the tongue lift-finger sweep method (option a) is not recommended as it can potentially push the obstruction further down the airway. Option c, using only head tilt, may not fully open the airway.
Option d, using a mask, can be used in situations where mouth-to-mouth rescue breathing is needed, but it is not the best first step for opening the airway.