​For a resource to be able to generate sustained competitive advantage over rivals,it must be

A) ​Valuable
B) Rare
C) Difficult to imitate or substitute away from
D) ​All of the above

For a resource to generate sustained competitive advantage over rivals, it must possess all three characteristics:
A) It must be valuable, meaning it must be able to enable the firm to exploit opportunities or reduce threats.
B) It must be rare, meaning it must be unique or scarce compared to rival firms.
C) It must be difficult to imitate or substitute away from, meaning rivals cannot easily replicate or replace the resource. Therefore, the best choice is D, which includes all three factors.