Final answer:
The pharynx is the feature used by both the respiratory and digestive systems, serving as a pathway for both air and food. option b.
Step-by-step explanation:
The feature used by both the respiratory and digestive systems is the pharynx. The pharynx, or throat, is a tube-like structure that performs dual functions. It serves as a passageway for air to travel from the nasal cavity to the larynx, and for food to travel from the mouth to the esophagus. The pharynx has three sections: the nasopharynx, which is involved in breathing and speech, the oropharynx, and the laryngopharynx, both of which are used in both breathing and digestion. Involuntary muscle contractions in the pharynx prevent food from entering the air passageways during the process of swallowing, ensuring that materials are directed appropriately towards either the respiratory or digestive systems.