Ted Works in His Family's Bakery Business

Ted works in his family's bakery business. They supply bread and rolls to neighboring restaurants, and they have their own store front where they sell breads, rolls, pastries, cookies and cupcakes. Ted wants to start offering gluten free products. Customers have been asking for them and leaving when he tells them he doesn't have any. This idea reflects which one of Porter's five competitive forces?

A) threat of entry of new competitors
B) bargaining power of suppliers
C) bargaining power of customers
D) threat of substitute products
E) rivalry among existing firms in an industry