Recent studies indicate that using corn to produce biofuel in the United States reduces __ greenhouse gas emissions species biodiversity soil erosion water use food prices

The question is asking about the impact of using corn to produce biofuel in the United States. Biofuel is a type of fuel that is derived from living matter or waste. In this case, the living matter is corn. The options provided are greenhouse gas emissions, species biodiversity, soil erosion, water use, and food prices. Among these options, greenhouse gas emissions are known to be reduced by using corn to produce biofuel. This is because the process of producing biofuel from corn involves the conversion of carbon dioxide into fuel, which reduces the amount of carbon dioxide in the atmosphere and thus reduces greenhouse gas emissions. The other options, such as species biodiversity, soil erosion, water use, and food prices, are not directly related to the production of biofuel from corn.