Many scientists believe that the current period of global warming is related to increased levels of .
a. nitrogen in the earth's atmosphere.
b. radon being released from the earth's soil.
c. carbon dioxide in the earth's atmosphere.
d. hydrogen in the outermost layer of the earth's atmosphere.

Although china’s total economic output, measured by gross domestic product (gdp), is third largest in the world, it is considered a developing nation. what is most likely the most important factor for this designation? a. china’s government spends money on things that do not benefit human development. b. china has a large population, so its gdp per person is only modest. c. china has a strong economy but weak literacy and school attendance rates. d. china’s high rates of disease offset the country's economic gains.