Which description of resource theory is most accurate? a. A resource is strategic to the extent that it is valuable, unusual, affordable, and non-substitutable. b. A resource is strategic to the extent that it is valuable, rare, affordable, and substitutable. c. A resource is strategic to the extent that it is valuable, unusual, difficult to imitate, and substitutable. d. A resource is strategic to the extent that it is valuable, rare, difficult to imitate, and non-substitutable