The following cereals should be avoided in patients with celiac diseases, except -: (A) Wheat, (B) Barely, (C) Maize, (D) Rye
Answer is C. Celiac disease (celiac sprue / gluten-sensitive enteropathy)

Celiac disease is a chronic disease, in which there is a characteristic mucosal lesion of the small intestine and impaired nutrient absorption, which improves on withdrawal of wheat gliadins and related grain proteins from the diet.
The fundamental disorder in celiac sprue is sensitivity to gluten which is alcohol soluble, water-insoluble protein component. It is found in wheat and closely related grains such as oat, barley and rye.
Celiac disease presents with features of malabsorption and the characteristic is that withdrawal of gluten-containing substances from the diet i.e. (wheat, oat, barley and rye) produces a dramatic improvement in the disease.