Here's a problem to solve: 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?

Among the 4 following options, which is the correct answer?

- 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
 