Which of the following statements is true of s-curves in technological improvement? multiple choice a)they typically show that technology goes through initial accelerated improvement, then diminishing improvement, then slow improvement. b) the s-curves flatten when the cost of each marginal improvement increases and diminishing returns to effort begin to set in. c) s-curves in technology diffusion and s-curves in technology performance are fundamentally the same process. d) they are obtained by plotting the cumulative number of adopters of the technology against time.