Task: Question Answering
Input (English): Scientists at a local university have been studying the impact that people have on Earth. One of the areas being studied is how the burning of fossil fuels affects the environment. Which effect of fossil fuel burning have the scientists most likely evaluated?  
 (A) the production of nitrogen-fixing bacteria (B) the mechanical weathering of roads (C) the formation of acid rain (D) the increase in runoff
Output (English): C