Investment in Innovation Is Often Considered to Have Increasing Marginal

Investment in innovation is often considered to have increasing marginal returns because

A) after the initial investment is made, subsequent investors face more difficult and expensive production problems.
B) of market development costs and the "public good" nature of knowledge.
C) innovation is mostly through "leaning by doing".
D) new products increase firms' profits.
E) R&D costs are negligible relative to firms' total costs.