Which of the following is a drawback of Porter's five forces model?

Group of answer choices

a. The model describes competition narrowly as a firm's closest competitors.

b. Managers cannot determine the changing speed of an industry or the rate of innovation.

c. It fails to provide a basis for deriving implications for a firm's strategic position within an industry.

d. The model fails to consider that threat of substitutes can come from outside a given industry.