Task: Question Answering
Input (English): Background Paragraph: In many ways, bacterial metabolism provides traits that are useful for ecological stability and for human society. One example is that some bacteria have the ability to fix nitrogen gas using the enzyme nitrogenase. This environmentally important trait can be found in bacteria of most metabolic types listed above. This leads to the ecologically important processes of denitrification, sulfate reduction, and acetogenesis, respectively. Bacterial metabolic processes are also important in biological responses to pollution; for example, sulfate-reducing bacteria are largely responsible for the production of the highly toxic forms of mercury (methyl- and dimethylmercury) in the environment. Non-respiratory anaerobes use fermentation to generate energy and reducing power, secreting metabolic by-products (such as ethanol in brewing) as waste. Facultative anaerobes can switch between fermentation and different terminal electron acceptors depending on the environmental conditions in which they find themselves. 
Story: Two regions, region A and region B, shared a common border, a river. Region A was favorable for sulfate-reducing bacteria and nitrogen fixing bacteria, while region B was more favorable for the developement of Non-respiratory anaerobes and facultative anaerobes. 
Question: Which region had more bacteria that used the enzyme nitrogenase?
Output (English): region A.