**Core Concept**
Crohn's Disease is a type of inflammatory bowel disease (IBD) characterized by chronic inflammation of the gastrointestinal tract. It can affect any part of the GI tract, from the mouth to the anus, but it most commonly affects the terminal ileum and the beginning of the colon.

**Why the Correct Answer is Right**
The terminal ileum is the most common site affected by Crohn's Disease because of its rich blood supply and the presence of lymphoid tissue, which is thought to play a role in the disease's pathogenesis. The terminal ileum is also the site where the ileum and jejunum meet, making it a common site for Crohn's Disease to cause narrowing and obstruction.

**Why Each Wrong Option is Incorrect**
**Option A:** The stomach is less commonly affected by Crohn's Disease, as it is more commonly associated with other types of gastritis or peptic ulcer disease.
**Option B:** The small intestine, while affected in Crohn's Disease, is more commonly affected in the proximal jejunum rather than the entire length.
**Option C:** The rectum is more commonly affected by Ulcerative Colitis, another type of IBD.

**Clinical Pearl / High-Yield Fact**
Crohn's Disease can affect any part of the GI tract, but it most commonly affects the terminal ileum, where it can cause narrowing and obstruction. This is an important fact to remember when evaluating patients with Crohn's Disease.

**Correct Answer:** C.