**Core Concept**
Ulcerative colitis (UC) is a type of inflammatory bowel disease (IBD) characterized by chronic inflammation and ulcers in the colonic mucosa. The exact pathogenesis of UC is multifactorial, involving an interplay between genetic predisposition, environmental factors, and an abnormal immune response.

**Why the Correct Answer is Right**
Ulcerative colitis is a chronic condition that primarily affects the colon, with symptoms including bloody diarrhea, abdominal pain, and weight loss. The disease is characterized by the presence of **inflammatory cells**, such as neutrophils and macrophages, in the colonic mucosa. The **loss of goblet cells** in the colonic epithelium also contributes to the disease's pathogenesis. Additionally, **predisposition to colorectal cancer** is a well-known complication of long-standing UC.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because **ulcerative colitis is not limited to the rectum**, as it can affect any part of the colon. While the rectum is often involved, the disease can extend proximally to involve the entire colon.

**Option B:** This option is incorrect because **ulcerative colitis is not primarily caused by a bacterial infection**, although the gut microbiome plays a significant role in the disease's pathogenesis. The exact cause of UC remains unknown, but it is believed to result from a combination of genetic, environmental, and immune system factors.

**Option C:** This option is incorrect because **ulcerative colitis is not typically characterized by skip lesions**, which are more commonly seen in Crohn's disease. In UC, the inflammation is typically continuous and involves the entire colon.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of UC is the presence of **pseudopolyps**, which are areas of regenerating mucosa that can be seen during endoscopy. These pseudopolyps can be a source of bleeding and can make the diagnosis of UC more challenging.

**Correct Answer:** None of the above