**Core Concept**
Moure's sign is a clinical finding associated with a specific type of head and neck cancer. It is characterized by the presence of a unilateral vocal cord paralysis or fixation due to invasion of the recurrent laryngeal nerve by a tumor. This sign is particularly relevant in the context of ENT (Ear, Nose, and Throat) pathology.

**Why the Correct Answer is Right**
The recurrent laryngeal nerve, which innervates the vocal cord, passes through the larynx and is closely associated with the postcricoid region. In postcricoid carcinoma, the tumor can invade the recurrent laryngeal nerve, leading to unilateral vocal cord paralysis or fixation. This is a classic presentation of Moure's sign, which is often observed in patients with postcricoid carcinoma. The proximity of the tumor to the recurrent laryngeal nerve in this region makes it more susceptible to nerve invasion.

**Why Each Wrong Option is Incorrect**
**Option A:** Nasopharyngeal carcinoma typically presents with symptoms such as nasal obstruction, epistaxis, and conductive hearing loss, but it is less likely to cause vocal cord paralysis directly.

**Option B:** Oropharyngeal carcinoma can cause symptoms such as dysphagia, neck mass, and voice changes, but it is less commonly associated with vocal cord paralysis due to direct nerve invasion.

**Option D:** Supraglottic carcinoma can cause symptoms such as dyspnea, stridor, and voice changes, but it is less likely to cause vocal cord paralysis due to direct nerve invasion, as the recurrent laryngeal nerve is not as closely associated with this region.

**Clinical Pearl / High-Yield Fact**
Moure's sign is a classic clinical finding in postcricoid carcinoma, and its presence should raise suspicion for this diagnosis in patients with head and neck cancer. A high index of suspicion and thorough clinical evaluation are essential in diagnosing this condition.

**✓ Correct Answer: C. Postcricoid carcinoma**