The correct answer is a model of mountain formation.
Explanation:
A model signifies towards a demonstration of a process, an idea, or a system that is used to illustrate a particular procedure, which cannot be experienced straightforwardly. The models are generally used in science to illustrate various procedures. When one is speaking about an appropriate model to demonstrate an incident, which takes place gradually, the most likely choice from the mentioned options will be a model of mountain formation. This is due to the fact that the procedure of mountain formation takes place very gradually over an extended time duration.
