Aforce that slowly wears away mountains and other features on the surface of earth is. . a..constructive. b. destructive. c. superposition. d. unnatural .

The answer is destructive force. 
Constructive force is the force that makes or forms the mountains and other features. Superposition forces are topics to be discussed in theories in physics and systems and may not be applicable here. Unnatural is just an unusual choice. 

Answertropical depression;

Answer cratons