**Core Concept**
A cyst and a granuloma are two distinct pathological entities with different underlying pathologies. A cyst is a fluid-filled or semi-solid structure enclosed by epithelial or connective tissue, often resulting from abnormal cell growth or fluid accumulation. On the other hand, a granuloma is a collection of immune cells, typically macrophages, that form in response to chronic inflammation or infection.

**Why the Correct Answer is Right**
The correct answer is based on the histological characteristics of these two lesions. A cyst typically has an epithelial lining, whereas a granuloma consists of a collection of immune cells, including macrophages, lymphocytes, and sometimes giant cells. The presence of an epithelial lining in a cyst is a key distinguishing feature from a granuloma.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the fundamental difference between a cyst and a granuloma. While both lesions can be caused by infection or inflammation, their histological characteristics are distinct.
**Option B:** This option is incorrect because it is too vague and does not provide a clear distinguishing feature between a cyst and a granuloma.
**Option C:** This option is incorrect because it is not a reliable method for differentiating between a cyst and a granuloma. While some cysts may be calcified, this feature is not unique to cysts and can be found in other lesions as well.

**Clinical Pearl / High-Yield Fact**
When diagnosing a cyst or granuloma, it is essential to consider the patient's clinical presentation, medical history, and imaging findings. A thorough histological examination of the lesion is often necessary to differentiate between these two entities.

**Correct Answer:** C. Presence of an epithelial lining.