Which generic strategy does Porter believe is best?

a$)$ A low$-$cost$,$ industry$-$wide one because it attracts the most customers

b$)$ A low$-$cost$,$ segment$-$based focus because the low$-$cost increases the customer base, while the segment focus locks the customers in

c$)$ A differentiated, segment$-$based focus because customers will pay more for unique, targeted products

d$)$ No one specific strategy is 'best'; Porter's model is just meant to get managers to think.