**Core Concept**

Celiac disease is an autoimmune disorder triggered by the ingestion of gluten, a protein found in wheat, barley, and rye. In patients with celiac disease, exposure to gluten leads to an immune response that damages the lining of the small intestine, impairing its absorption of nutrients. Avoiding gluten is essential for managing the disease and preventing complications.

**Why the Correct Answer is Right**

The correct answer, **D**, represents a cereal that is gluten-free and safe for patients with celiac disease. Oats are generally considered gluten-free and can be consumed in moderation by patients with celiac disease, as long as they are processed in gluten-free facilities and certified gluten-free. The other options are not gluten-free and should be avoided in patients with celiac disease.

**Why Each Wrong Option is Incorrect**

A. Wheat (Hexose) contains gluten and should be avoided. Hexose refers to glucose, which is a sugar, not a specific cereal.

B. Rye is another cereal that contains gluten and should be avoided in patients with celiac disease.

C. Barley is a cereal grain that contains gluten and should be avoided in patients with celiac disease.

**Clinical Pearl / High-Yield Fact**

In clinical practice, it is essential to educate patients with celiac disease about the importance of adhering to a gluten-free diet. Ensuring proper nutrition and preventing complications is crucial for their overall health management.

**Correct Answer Explanation**

Avoiding gluten from wheat, barley, and rye is crucial for patients with celiac disease. Oats, when certified gluten-free, can be safely consumed.