**Core Concept**
The thymus is a **lymphoid organ** responsible for the maturation and selection of T-lymphocytes. Histologic examination of the thymus can reveal various features, including **reactive follicles** and **germinal centers**, which are indicative of immune responses.

**Why the Correct Answer is Right**
Reactive follicles with germinal centers in the thymus are characteristic of **thymic hyperplasia** or **thymitis**, which can occur in response to various stimuli, including autoimmune disorders or infections. The presence of these features suggests an immune response, with **B-lymphocytes** and **T-lymphocytes** interacting in the thymus.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not a recognized condition associated with reactive follicles in the thymus.
**Option B:** Incorrect as it does not typically present with reactive follicles in the thymus.
**Option C:** Incorrect because it is not characterized by the presence of germinal centers in the thymus.

**Clinical Pearl / High-Yield Fact**
The presence of **germinal centers** in the thymus is a key feature of **thymic hyperplasia**, which can be associated with **myasthenia gravis** or other autoimmune disorders.

**Correct Answer:** D. Thymic hyperplasia