18) The earth's atmosphere is mainly heated by (2pts) infrared light radiated by the sun. O visible light radiated by the sun. hot exhaust gases from burning fossil fuels. infrared light radiated by the earth. 19) Of the following greenhouse gases, the least important (2pts) is/are carbon dioxide. methane CFC and HCFC refrigeration gases. nitrous oxide. 20) The two countries together responsible for about 40 percent of the world's carbon dioxide (2pts) emissions are the United States and Russia. Russia and China the United States and India. the United States and China, 21) After electricity generation and heating, the next most important contribution to greenhouse (2pts) gases in the atmosphere comes from transport deforestation. O agriculture O industry 22) Two-thirds of the world's oil production is used for (2pts) O. chemical products. electricity generation . O transport fuel. O heating. 23) Methane is the chief constituent of (2pts)