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current extinction rate over, for example, the last two decades. What they have found is startling.According to cautious estimates, the current extinction rate is __________ times greater than thebackground rate.A. 20 B. 50 C. 100 D. 300 Question 19 of 405.0/ 5.0 PointsPhytoplankton, aside from being the base of the oceanic food chain, produce __________ percent of our planet’s atmospheric oxygen.
Question 20 of 400.0/ 5.0 PointsWhich of these atmospheric layers enables radio transmissions?
Part 2 of 2 - 80.0/ 100.0 PointsQuestion 21 of 405.0/ 5.0 PointsAs a demographer, within a specific population I compare the number of economically productive people between the ages of 15 and 64 with the number of people younger than 15 and older than 64 who, in general, rely on the productive people for sustenance. The measure I’m calculating is normally referred to as the:Question 22 of 400.0/ 5.0 PointsOur brief discussion of China during Mao Zedong’s Great Leap Forward in 1959 to 1960 was meant to illustrate the:
A. fact that population growth does not necessarily proceed at a steady rate. B. importance of economic policies in sustaining population growth. C. irrelevance of political and economic factors in regard to population growth. D. ever-present danger of unrestrained population growth. Question 23 of 405.0/ 5.0 PointsIn which country have death rates declined markedly even as infant mortality rates are the highest in the world?
Question 24 of 405.0/ 5.0 PointsIn the context of transition theory, the main factor in the reduction of death rates is:Question 25 of 405.0/ 5.0 PointsIn the United States, in the decades following World War II, birth rates increased enormously. This is an example of __________ effects that may impact population growth.