## Core Concept
Meckel's diverticulum is a congenital diverticulum of the small intestine, resulting from the incomplete closure of the vitelline duct during fetal development. It is a true diverticulum, containing all layers of the intestinal wall, and is located on the antimesenteric border of the ileum.

## Why the Correct Answer is Right
The correct answer is related to the characteristics of Meckel's diverticulum. Typically, Meckel's diverticulum is located within 2 feet of the ileocecal junction, is a true diverticulum (containing all layers of the intestinal wall), and can contain ectopic gastric or pancreatic tissue. The presence of ectopic tissue, particularly gastric mucosa, can lead to complications such as gastrointestinal bleeding.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically, Meckel's diverticulum is found within 2 feet of the ileocecal junction, making statements about its usual location incorrect if they suggest otherwise.
- **Option B:** If a statement suggests it's not a true diverticulum, that would be incorrect because Meckel's diverticulum does contain all layers of the intestinal wall, qualifying it as a true diverticulum.
- **Option C:** If an option mentions that it does not contain ectopic tissue, that would be incorrect because Meckel's diverticulum can indeed contain ectopic gastric or pancreatic tissue.
- **Option D:** Without specific details on option D, we assume its incorrectness based on the provided correct answer.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that Meckel's diverticulum can cause gastrointestinal bleeding, especially in children, due to the presence of ectopic gastric mucosa. The "rule of twos" is often remembered: it occurs in 2% of the population, is usually located within 2 feet of the ileocecal junction, and often presents with symptoms before the age of 2.

## Correct Answer: D.