Which natural resource is important to the desert region and mountain region?

Minerals are the important natural resource.
In desert regions or arid lands, it can be found rich mineral deposits as result of high evaporation. When there are lakes or water formations due to eventual water deposition, they lead to high concentrate mineral sources of minerals such as gypsum, borates, and salts.
In mountain regions, there can be often found minerals, and mining is often present. 

Tropical climate is experienced in the nothern countries of south america

The correct answer is a)  a resource with a limited supply; it will run out.