**Core Concept**
The sphenoidal sinus is one of the paranasal sinuses located within the body of the sphenoid bone. It plays a crucial role in the drainage and ventilation of the nasal cavity. Understanding the anatomy of the sphenoidal sinus and its relationship with the surrounding structures is essential for the diagnosis and management of various nasal and sinus disorders.

**Why the Correct Answer is Right**
The sphenoidal sinus opens into the spheno-ethmoidal recess, which is a small, posteriorly located recess in the nasal cavity. This recess is situated above the superior concha and is connected to the sphenoidal sinus through a narrow passage. The spheno-ethmoidal recess is a critical area for the drainage of the sphenoidal sinus, and any obstruction in this area can lead to sinusitis and other complications.

**Why Each Wrong Option is Incorrect**
**Option A:** The superior meatus is a passage in the nasal cavity that receives drainage from the posterior ethmoidal cells and the sphenoid sinus via the spheno-ethmoidal recess, but it is not the primary opening of the sphenoidal sinus. The superior meatus is located above the superior concha and is not directly connected to the sphenoidal sinus.

**Option B:** The inferior meatus is a passage in the nasal cavity that receives drainage from the nasolacrimal duct and the posterior nasal apertures, but it is not related to the sphenoidal sinus. The inferior meatus is located below the inferior concha and is not a suitable opening for the sphenoidal sinus.

**Option C:** The middle meatus is a passage in the nasal cavity that receives drainage from the frontal, anterior ethmoidal, and maxillary sinuses, but it is not the primary opening of the sphenoidal sinus. The middle meatus is located between the middle and inferior nasal conchae and is not directly connected to the sphenoidal sinus.

**Clinical Pearl / High-Yield Fact**
The spheno-ethmoidal recess is a critical area for the drainage of the sphenoidal sinus, and any obstruction in this area can lead to sinusitis and other complications. It is essential for clinicians to be aware of the anatomy of the sphenoidal sinus and its relationship with the surrounding structures to diagnose and manage various nasal and sinus disorders effectively.

**✓ Correct Answer: D. Spheno-ethmoidal recess**