Gluten is formed when two proteins known as glutenin and gliadin are moistened and kneaded together. What is the source of these proteins?

The correct answer is wheat flour because it is the primary source of gluten, which is a protein complex formed when glutenin and gliadin are mixed together with water and manipulated through kneading. Wheat flour contains a high proportion of these proteins, which are essential for creating the elasticity and structure that is characteristic of many baked goods, such as bread and pasta.

Other flours, such as rice flour, corn flour, and barley flour, either contain much lower levels of gluten-forming proteins or do not contain them at all. As a result, they do not develop gluten in the same way that wheat flour does, which is why these alternatives are often used in gluten-free baking or for specific culinary applications where gluten development is not desired.