Answer: d. Two phone providers, each offering benefits to customers who switch to its service
Explanation:
Monopolistic competition occur when there are many firms producing different products which has close substitutes, that is the products are similar. Also, products are known or recognised based on their quality or design and producers are free to enter or exit because there are no barriers. Hence, advertisement is used in promoting sales of goods and services and firms tend to lower prices in order to sell their goods.