**Core Concept**
Ulcerative colitis is a type of inflammatory bowel disease characterized by chronic inflammation and ulceration of the colonic mucosa. The definition of ulcerative colitis involves several key factors, including the extent of disease, depth of inflammation, and presence of specific symptoms.

**Why the Correct Answer is Right**
Since the options are not provided, let's discuss the general criteria used to define ulcerative colitis. The disease is typically defined by the presence of chronic inflammation, ulceration, and a specific pattern of involvement, usually starting from the rectum and extending proximally.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option, we can't comment on its correctness.
**Option B:** Similarly, without the specific option, we can't comment on its correctness.
**Option C:** Again, without the specific option, we can't comment on its correctness.
**Option D:** This option is also not provided for comment.

**Clinical Pearl / High-Yield Fact**
A key point to remember in ulcerative colitis is that it typically involves the rectum, with inflammation extending proximally in a continuous manner.

**Correct Answer:** D. Skip lesions