The united states has natural resources plus:
a. no problems
b. from u. n.
c. technical skills
only pick one, this isn't a hard question, 15 points to who ever figures it out.

C. technical skills

Explanation:

The United States are one of the richest countries in the world when it comes to natural resources. This vast country has anything from oil and natural gas, to lumber and water, to fertile soil and minerals.

It is not just to posses the natural resources though, but the country also has to have lot of people with technical skills so that those resources can be used. The people in the United States, in general, posses the technical skills required for exploitation of the natural resources, which is no wonder when taken in account that big portion of the population has solid education.

This contributes to this country being the biggest economy in the world, as the enormous amount of natural resources, combined with the skillful labor force, results in lot of development, production, and profit.