I would go with 4 that's what makes the most sense to me, and i just learned about this last year so... I hope this helps good luck..
They are all rock with different size and shapes and are located in different areas possibly in the same areas but they all have there own unique textures from the photographs and 3 of them look like maybe a fossil of some type of when the dinosaurs where still around and the rocks on the top left corner look smooth and are a small type of igneous rocks. That have been soothed over the years.
It's Mutualism, since they share a mutual relationship
It can be polluted by waters bottles plastic bottles etc going into the ocean
