Final answer:
Obstruction of the airway poses the greatest risk to a child or elderly person.
Step-by-step explanation:
The item that poses the greatest risk to a child or elderly person would be obstruction of the airway. Young children, in particular, are prone to choking on small objects or foods that can adapt their shape to the pharynx, such as bananas and marshmallows. However, this risk also extends to adults. It is important to supervise young children and to be cautious when consuming food that could potentially cause choking.