Answer:
A. Abrasion
Explanation:
<em>"In abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a mountainside or cliff. Moving water causes abrasion as particles in the water collide and bump against one another."</em>
<em>-Lumen Learning</em>
An irregularly occurring and complex series of climatic changes affecting the equatorial pacific region and beyond every few years, characterized by the appearance of unusually warm, nutrient-poor water off northern Peru and Ecuador, typically in late December
I think its Multicellular Organisms,., i could be wrong
Natural system is former when various components get grouped together for a particular function