I think the correct answer is the first option. The action that would be most effective in decreasing the amount of carbon dioxide in the atmosphere while increasing the amount of biodiversity in an area would be planting more trees to absorb more of the carbon dioxide from the atmosphere. Turning forests into housing developments would destroy biodiversity and would increase carbon dioxide. Digging prairies would probably affect the amount of carbon dioxide but it would only have minimal change. Sowing beans and legumes would involve using equipment which will produce more carbon dioxide. So, option A is the best answer.
