Self-regulating of population numbers acts only when the population is:
a. large
b. declining
c.threatened
d. stable
e. small

C, since when you are threatened, you try to team up with others to be safe.

I think you forgot to give the options along with the question. I am answering the question based on my knowledge. Appalachian mountain range is well known for providing coal, copper and iron. Any of these choices can be your answer. Coal is actually the most abundant. I hope that the answer helps you.