**Core Concept**
Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by recurrent abdominal pain, changes in bowel habits, and passage of mucus in stool, often exacerbated by stress. The absence of blood in stool and the presence of mucus distinguish IBS from inflammatory bowel diseases.

**Why the Correct Answer is Right**
The correct answer is A. Irritable bowel syndrome because the patient's symptoms align with the diagnostic criteria for IBS, which include recurrent abdominal pain at least 1 day per week in the last 3 months, associated with 2 or more of the following: change in stool frequency, change in stool consistency, and passage of mucus. The absence of blood in stool and the presence of mucus suggest a non-inflammatory cause, consistent with IBS.

**Why Each Wrong Option is Incorrect**
**Option B:** Ulcerative Colitis is an inflammatory bowel disease characterized by bloody diarrhea, which is not present in this patient. Ulcerative Colitis also typically involves the rectum and extends proximally in a continuous manner.

**Option C:** Crohn's disease is another inflammatory bowel disease that can cause abdominal pain, diarrhea, and weight loss, but it often involves the terminal ileum and may present with complications such as fistulas or abscesses.

**Option D:** Amebiasis is an infectious disease caused by Entamoeba histolytica, which typically presents with bloody diarrhea, weight loss, and abdominal pain, and is not typically associated with passage of mucus in stool.

**Clinical Pearl / High-Yield Fact**
The Rome IV criteria provide a standardized approach to diagnosing functional gastrointestinal disorders, including IBS. These criteria include a combination of symptoms, such as abdominal pain, changes in bowel habits, and passage of mucus, and exclude other causes of symptoms.

**✓ Correct Answer: A. Irritable bowel syndrome**