Answer: E. The firm's ability to differentiate its product
Explanation:
The factor under the control of owners and managers that make a firm successful and allow it to earn economic profits is the firm's ability to differentiate its product.
Product Differentiation has to do with making a product unique from that of its rivals so that it'll be attractive to the customers and the target market. This will slow be vital for the company to produce at a average cost that is lower than that of its competing firms. This will help the company to have a competitive edge over others.