Firms are likely to underinvest in research and development, which slows knowledge capital, slowing economic growth, because
A. knowledge capital is both rival and excludable, and no other firms can freely access the research and development of one particular firm
B. they can save that money and invest in capital accumulation, which is much better for growth
C. research and development are expensive and at the firm level, it is subject to increasing returns
D. knowledge capital is both nonrival and nonexcludable; other firms can freely access the research and development of one particular firm
Answer: D