Answer:
**b. architecture
Explanation:
Saint-Denis is primarily known for its architectural innovation, specifically in the context of its abbey, which was the first major structure whose design utilized Gothic architecture elements. This architectural style introduced features like pointed arches, ribbed vaults, and flying buttresses, which allowed for higher ceilings, larger windows, and more light-filled interiors.
Therefore, the best answer to the question regarding what innovation is attributed to Saint-Denis is:
**b. architecture**
This choice directly relates to the significant contributions made by the Abbey of Saint-Denis to the development and spread of Gothic architecture during the medieval period.
