**Core Concept**
The question is testing the concept of the relationship between appendicectomy and the development of certain conditions. Appendicectomy, or the surgical removal of the appendix, is a procedure often performed to treat acute appendicitis. Research has shown that individuals who have undergone appendicectomy may have a reduced risk of developing certain conditions.

**Why the Correct Answer is Right**
The correct answer is related to the hypothesis that appendicectomy may reduce the risk of developing diverticulitis. This is because the appendix and the large intestine share a common embryological origin, and some researchers suggest that the appendix may act as a reservoir for bacteria that can cause diverticulitis. By removing the appendix, the risk of bacterial overgrowth and subsequent diverticulitis may be reduced.

**Why Each Wrong Option is Incorrect**
* **Option A:** There is no established link between appendicectomy and a reduced risk of peptic ulcer disease.
* **Option B:** While appendicectomy may reduce the risk of certain complications, there is no evidence to suggest that it reduces the risk of cholecystitis.
* **Option C:** Appendicectomy does not have a proven effect on the risk of colon cancer.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the relationship between appendicectomy and the development of certain conditions is still being studied, and more research is needed to fully understand the potential benefits and risks of this procedure.

**Correct Answer: D. Diverticulitis**