Task: Question Answering
Input (English): Animals can affect their habitats through activities of finding food and raising their young. Sometimes these activities have a positive effect on the habitat of other organisms. Which is the best example of an activity that has a positive effect?  
 (A) elephants stripping bark from trees (B) viruses infecting the cells of certain birds (C) beavers constructing dams to make ponds for lodges (D) semi-aquatic rodents feeding on the roots of aquatic plants
Output (English): C