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
I am hesitating between 4 options to answer the following question, which option should I choose?
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?
Possibilities:
- 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

beavers constructing dams to make ponds for lodges