Final answer:
The internal nares open into the nasopharynx, which is a part of the pharynx exclusive to breathing and speech.
Step-by-step explanation:
The internal nares open into the nasopharynx, which is the upper part of the pharynx situated above the soft palate. The pharynx is a shared anatomical structure for both the respiratory and digestive systems and has three subdivisions: the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx deals exclusively with breathing and speech, while the oropharynx and laryngopharynx have functions in both breathing and digestion. The most superior of these, the nasopharynx, begins posterior to the nasal cavities and connects to the oropharynx below. The laryngopharynx then continues inferiorly, connecting to the esophagus posteriorly and the larynx anteriorly, leading air into the bronchial tree. Therefore, the internal nares open into option d. Nasopharynx.