Most grocery stores carry a wide variety of national brands in addition to their own private-label brands. The private-label brands are often made by the same national brands they are competing with. Which type of strategy is a firm using when it creates a lower-priced private-label brand in addition to its other, higher-priced brands? 

a. Portfolio management 

b. Distinctive competence 

c. Focus 

d. Cost leadership 

e. Differentiation