Answer:
D. Chest compressions
Step-by-step explanation:
A is clearly wrong. Slapping an individual who is not breathing will do nothing except harm.
B is silly. Neck massages could actually harm the person's airways, and won't help.
C is unimportant. Not only does an ice bath take forever to prepare, meaning the adult would be long dead, but they could also accelerate the person's death because they increase the amount of energy the person would have to use to function.