**Core Concept**
Hyperplasia refers to an increase in the number of cells in a tissue or organ, leading to an expansion of the tissue's size. This is often a response to increased demand or growth stimulus. In contrast, metaplasia involves a change in the type of cells, often in response to injury or environmental stress.

**Why the Correct Answer is Right**
Hyperplasia is a characteristic feature of the menstrual cycle, where the endometrium undergoes thickening and shedding under the influence of estrogen and progesterone. The correct answer involves an increase in the number of cells in the endometrium, leading to an alteration in the thickness of the endometrial lining. This process is essential for preparing the uterus for a potential pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it involves a change in the type of cells, which is characteristic of metaplasia. For example, the transformation of squamous epithelium to columnar epithelium in the esophagus is a classic example of metaplasia.
**Option B:** This option is incorrect as it involves a decrease in the number of cells, which is characteristic of atrophy.
**Option C:** This option is incorrect as it involves a change in the type of cells, which is characteristic of metaplasia. For example, the transformation of cuboidal epithelium to squamous epithelium in the skin is a classic example of metaplasia.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that hyperplasia and metaplasia are distinct histological changes, and understanding the differences between them is crucial for diagnosing and managing various conditions.

**Correct Answer:** C.