**Core Concept:** Lower gastrointestinal (GI) bleeding is a condition where blood loss occurs in the region of the large intestine and rectum. Common causes include various pathologies affecting the lower GI tract.

**Why the Correct Answer is Right:** Hemorrhoids (Option C) are the most common cause of lower GI bleeding in adults. Hemorrhoids are swollen blood vessels in the rectum and anus due to increased blood flow, straining, or prolonged pressure. They can lead to bleeding during or after defecation, which is usually painless and visible in the toilet or on a tissue.

**Why Each Wrong Option is Incorrect:**

A. Gastritis (Option A) and ulcerative colitis (Option B) are related to upper GI tract bleeding and do not typically cause lower GI bleeding.

Diverticulitis (Option D) is a less common cause of lower GI bleeding, usually associated with inflammation and infection of the diverticula, which are small pouches that form when the lining of the colon becomes weak.

**Clinical Pearl:** Hemorrhoids can be managed conservatively with lifestyle modifications, such as avoidance of straining, weight loss, and maintaining a balanced diet rich in fiber. In severe cases, surgery may be required.

**Correct Answer:** **C. Hemorrhoids** are the most common cause of lower gastrointestinal bleeding in adults, resulting from increased blood flow, straining, or prolonged pressure. They are easily managed with conservative measures and rarely require surgery.