People are willing to pay a higher price if they believe that supplies are
a. flunctuating
b. endless
c. limited
d. increasing

C. Limited

If you have a small amount of product/resources that means that it is rare, and therefore more valuable.

For example, in the U.S. economy, there is a limited amount of currency, and that is what makes the currency valuable.

Or the better example, in a game like Minecraft, the resource "diamond ore," is only worth value to the player because it is a Limited resource, and it does not spawn often.

Hope this helps!

What do you mean by that?