**Core Concept**
Trachoma is a chronic keratoconjunctivitis caused by Chlamydia trachomatis, leading to various stages of ocular and systemic involvement. Trachoma Stage III is characterized by intense inflammation and scarring of the conjunctiva, resulting in severe complications.

**Why the Correct Answer is Right**
Pannus is a feature of Trachoma Stage I and II, where it represents the active inflammation of the conjunctiva. It is characterized by the growth of blood vessels on the surface of the conjunctiva, resulting from the release of angiogenic factors. In contrast, Trachoma Stage III is marked by scarring and cicatrization, making pannus an incorrect feature of this stage. The correct features of Trachoma Stage III include the formation of Herbe's pits, which are small depressions on the surface of the conjunctiva resulting from scarring.

**Why Each Wrong Option is Incorrect**
**Option A:** Herbe's pits are a characteristic feature of Trachoma Stage III, resulting from the intense scarring and cicatrization of the conjunctiva. This makes Herbe's pits a correct feature of this stage.
**Option C:** Necrosis in scar is a possible complication of Trachoma Stage III, where the intense scarring and cicatrization can lead to ischemia and necrosis of the conjunctiva. This makes necrosis in scar a plausible feature of this stage.
**Option D:** Scar on tarsal conjunctiva is a hallmark of Trachoma Stage III, representing the intense scarring and cicatrization of the conjunctiva. This makes scar on tarsal conjunctiva a correct feature of this stage.

**Clinical Pearl / High-Yield Fact**
In Trachoma Stage III, the intense scarring and cicatrization of the conjunctiva can lead to complications such as entropion, trichiasis, and corneal opacity, ultimately resulting in blindness if left untreated.

**✓ Correct Answer: B. Pannus**