## **Core Concept**
The paranasal sinuses are air-filled cavities within the bones around the nasal cavity, and they communicate with the nasal cavity through various meatuses. The middle meatus is a critical area where several paranasal sinuses drain.

## **Why the Correct Answer is Right**
The correct answer involves identifying which paranasal sinuses open into the middle meatus. The middle meatus receives drainage from the **frontal (anterior ethmoidal) cells**, **maxillary sinus (via the semilunar hiatus)**, and **anterior ethmoidal cells**. The **maxillary sinus** opens into the middle meatus through the semilunar hiatus. The **frontal sinus** also drains into the middle meatus. **Anterior ethmoid cells** drain here as well.

## **Why Each Wrong Option is Incorrect**
- **Option C: Posterior ethmoid** - The posterior ethmoidal cells usually drain into the superior meatus, not the middle meatus.
- **Option E: Sphenoid** - The sphenoid sinus typically drains into the sphenoethmoidal recess, which is located above and posterior to the superior concha, not into the middle meatus.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **semilunar hiatus** in the middle meatus is a critical structure where the maxillary and frontal sinuses, along with anterior ethmoid cells, drain into the nasal cavity. This area is significant in sinusitis and surgical interventions.

## **Correct Answer:** D.