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Which of the following best describes generally observed trends in productivity? O A. Diminishing returns as more labour is added to a given stock of capital. O B. Productivity has increased significantly in rich countries but decreased in most other countries. C. Income per capita varies significantly across countries. O D. None of the above. Reset Selection Mark for Review What's This? Question 56 of 76 1 Points In endogenous growth models, technological innovation: O A. Is taken as given. O B. Depends on the incentives to self-interested entrepreneurs. O c. Can only benefit others if they are prepared to pay for it. O D. Depends on increases in the productivity of labour