9. What is the total amount in million metric of tons of carbon dioxide emitted by
petroleum in the year 2000?
A. 1000
B. 2200
C. 2800
D. 6800

10. The greenhouse effect is a natural phenomenon. Without a natural greenhouse
effect, the temperature of the Earth would be about -18°C instead of its present
14°C. Why are scientists concerned about the greenhouse effect?
I. There is no technology that will keep the temperature of Earth constant.
II. There is a significant change in Earth's temperature that leads to global
warming.
III. Human activities like burning of fossil fuels and deforestation enhance the
greenhouse effect.
IV. The human population is increasing rapidly; more carbon dioxide will be
released to the atmosphere.
A. I and II only
B. III and IV only
C. I, III and IV only
D. I, II, III, and IV​