### Core Concept
Rhinosporidiosis is a chronic, granulomatous infection caused by Rhinosporidium seeberi, a protozoan that typically affects the mucous membranes of the nose, eyes, and genitalia. The disease is characterized by the formation of polypoid masses that can lead to significant morbidity if left untreated.

### Why the Correct Answer is Right
Surgery is the primary treatment for rhinosporidiosis, as it allows for the complete removal of the infected tissue and prevents recurrence. This is particularly important in the nasal cavity, where the polyps can cause significant obstruction and lead to complications such as respiratory distress. The surgical approach typically involves excision of the polyp with a margin of healthy tissue, followed by histopathological examination to confirm the diagnosis.

### Why Each Wrong Option is Incorrect
**Option A:** Rhinosporidiosis is not caused by a fungus, but rather by a protozoan called Rhinosporidium seeberi. This distinction is critical in understanding the pathophysiology of the disease and developing effective treatment strategies.
**Option B:** While the polypoid masses associated with rhinosporidiosis can appear greyish in color, this characteristic is not unique to the disease and can be seen in other conditions as well. Therefore, relying solely on visual inspection to diagnose rhinosporidiosis is not sufficient.
**Option D:** Radiotherapy is not a treatment option for rhinosporidiosis, as the disease is caused by a living organism that requires surgical removal to prevent recurrence.

### Clinical Pearl / High-Yield Fact
It's essential to note that rhinosporidiosis can mimic other conditions such as nasal polyps or granulomatous diseases, making a definitive diagnosis critical. A high index of suspicion and histopathological examination of the excised tissue are crucial in making an accurate diagnosis.

### Correct Answer Line
✓ Correct Answer: C. Surgery is the treatment.