Final answer:
Mountain building is the best example of a natural process acting as a constructive force.
Step-by-step explanation:
The best example of a natural process acting as a constructive force is mountain building.
Mountain building occurs when tectonic forces push the Earth's crust upward, causing the formation of mountains. This process is typically associated with plate tectonics and occurs when two plates collide or when one plate is subducted beneath another.
Mountain ranges, such as the Himalayas and the Rocky Mountains, are the result of mountain building. These ranges provide important natural resources and habitats for various plant and animal species.