**Core Concept**
The maxillary sinus is a paranasal sinus located in the maxillary bone, and its drainage is through the semilunar hiatus, an opening in the lateral wall of the nasal cavity. The carcinoma in the nasal cavity would block the drainage of the maxillary sinus if it grows in a location that obstructs the hiatus.

**Why the Correct Answer is Right**
The semilunar hiatus is located in the middle meatus of the nasal cavity. The carcinoma would block the drainage of the maxillary sinus if it grows in the region of the middle meatus, specifically in the area of the nasolacrimal duct or the anterior ethmoidal cells. This would prevent the mucus from the maxillary sinus from draining into the nasal cavity through the semilunar hiatus.

**Why Each Wrong Option is Incorrect**
**Option A:** The anterior ethmoidal cells are located in the anterior part of the nasal cavity, but they are not directly related to the drainage of the maxillary sinus.
**Option B:** The posterior ethmoidal cells are located in the posterior part of the nasal cavity, and they drain into the superior meatus, not the middle meatus where the semilunar hiatus is located.
**Option C:** The nasopharynx is the upper part of the pharynx, and it is not directly related to the drainage of the maxillary sinus.

**Clinical Pearl / High-Yield Fact**
The paranasal sinuses, including the maxillary sinus, are important structures to consider in the diagnosis and treatment of nasal cavity cancers. The location and extent of the cancer can affect the choice of treatment and the outcome for the patient.

**Correct Answer:** C.