**Core Concept**
The paranasal sinuses are air-filled spaces around the nasal cavity that communicate with it through specific openings. The **ethmoidal sinuses** are a group of small air cells within the **ethmoid bone**.

**Why the Correct Answer is Right**
The **posterior ethmoidal sinuses** drain into the **superior meatus**. This is because the superior meatus is located between the **superior** and **middle nasal conchae** and receives the openings of the **posterior ethmoidal sinuses**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the anterior ethmoidal sinuses drain into the **middle meatus**.
**Option B:** Incorrect because the frontal sinus drains into the **middle meatus**.
**Option D:** Incorrect because the maxillary sinus also drains into the **middle meatus**.

**Clinical Pearl / High-Yield Fact**
Remember that the **middle meatus** is a common site for drainage of the **anterior ethmoidal sinuses**, **frontal sinus**, and **maxillary sinus**, while the **superior meatus** is associated with the **posterior ethmoidal sinuses**.

**Correct Answer:** C. posterior ethmoidal sinuses