question: 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?
choices.text: elephants stripping bark from trees viruses infecting the cells of certain birds beavers constructing dams to make ponds for lodges semi-aquatic rodents feeding on the roots of aquatic plants
choices.label: A B C D