## Core Concept
Celiac disease is an autoimmune disorder where the ingestion of gluten leads to damage in the small intestine. It is characterized by an immune reaction to **gluten**, a protein found in **wheat**, **barley**, and **rye**. Management involves a strict **gluten-free diet**.

## Why the Correct Answer is Right
Oats are often considered safe for individuals with celiac disease, but they can be contaminated with gluten during processing. However, pure oats that are gluten-free can be part of a gluten-free diet. The key here is that among the common cereals, oats are the least likely to contain gluten or cause a reaction in celiac patients, making option **D. Oats** the correct answer.

## Why Each Wrong Option is Incorrect
- **Option A: Wheat** - Wheat contains gluten and is one of the primary cereals that individuals with celiac disease must avoid.
- **Option B: Barley** - Barley also contains gluten and is harmful to patients with celiac disease.
- **Option C: Rye** - Rye is another gluten-containing cereal that should be avoided by individuals with celiac disease.

## Clinical Pearl / High-Yield Fact
A crucial point to remember is that patients with celiac disease must adhere strictly to a gluten-free diet to manage their condition effectively. This involves avoiding all products made from wheat, barley, and rye, and being cautious with oats due to potential cross-contamination.

## Correct Answer: D. Oats