**Core Concept**
Pseudomembranous colitis, also known as Clostridioides difficile (C. difficile) colitis, is a type of colitis caused by the bacterium C. difficile. This condition is characterized by the formation of pseudomembranes in the colon, leading to inflammation and damage to the intestinal lining.

**Why the Correct Answer is Right**
The correct answer is related to the pathogenesis of pseudomembranous colitis. C. difficile produces toxins A and B, which are responsible for the damage to the intestinal lining and the formation of pseudomembranes. Toxin A causes damage to the epithelial cells, leading to inflammation and tissue damage, while toxin B disrupts the cell wall of the bacteria, leading to further damage and the formation of pseudomembranes.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because C. difficile colitis is indeed caused by the bacterium C. difficile, and not by another type of bacteria.
* **Option B:** This option is incorrect because pseudomembranous colitis is indeed characterized by the formation of pseudomembranes in the colon, which are composed of inflammatory cells, bacteria, and cellular debris.
* **Option C:** This option is incorrect because C. difficile produces toxins A and B, which are responsible for the damage to the intestinal lining and the formation of pseudomembranes, not toxins C and D.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that C. difficile colitis is often associated with antibiotic use, which disrupts the normal gut flora and allows C. difficile to overgrow and produce toxins. This is why patients who have recently taken antibiotics are at increased risk of developing C. difficile colitis.

**Correct Answer:** A.