**Core Concept**
The paranasal sinuses are air-filled cavities around the nasal cavity, and their drainage is crucial for the prevention of infection and maintenance of normal nasal function. The **middle meatus** is a key area for drainage of these sinuses.

**Why the Correct Answer is Right**
The anterior and posterior ethmoidal sinuses, as well as the frontal sinus, drain into the **middle meatus** through the **semilunar hiatus**. The maxillary sinus also drains into the middle meatus.

**Why Each Wrong Option is Incorrect**
**Option A:** The frontal sinus indeed drains into the middle meatus.
**Option B:** The anterior ethmoidal sinuses also drain into the middle meatus.
**Option C:** The maxillary sinus drains into the middle meatus through the semilunar hiatus.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that the sphenoid sinus drains into the **superior meatus**, not the middle meatus.

**Correct Answer:** D. Sphenoid sinus.