14. An individual derives utility from consuming "all other goods," g, and clean air (measured by the reduction in particulate matter per m"), a, as measured by the utility function U(g, a) = gua* *. The price of consumer goods equals $20 and the price of clean air (abatement) equals $10. What is the slope of the Engel curve when income increases from $100 to $200? O A. The slope is - 25. O B. The slope is infinite. O C. The slope is zero. O D. The slope is 25