Within the food service industry​ (restaurants that serve meals to​ customers, but not just fast​ food), find examples of firms that have sustained competitive advantage by competing on the basis of​ (1) cost​ leadership, (2)​ response, and​ (3) differentiation. Cite one example in each​ category; provide a sentence or two in support of each choice. ​(​Hint: A ​"99cents ​menu" is very easily copied and is not a good source of sustained​ advantage.)