9. The United States has lost up to one-third of its original topsoil to erosion
ID: 296487 • Letter: 9
Question
9. The United States has lost up to one-third of its original topsoil to erosion, yet crop yields have not declined. This is because a. production has shifted to new regions with fresh soils. b. high yield crop varieties need fewer soil nutrients compared to their wild ancestors. soil eroded on site is usually deposited on a nearby field. fertilizers have replaced nutrients lost through erosion. c. 10. Growing crops specifically for biofuel production would probably result in a. reduced desertification. b. reduced usage of fertilizers and pesticides. c. reduced food production. d. reduced soil erosion. 11. The "pesticide treadmill" refers to a. soil erosion that leaches pesticides from application areas into groundwater b. insect mortality associated with pesticide use. c. natural selection in pests that increases their resistance to pesticides. d. loss of genetic diversity in crop varieties. 12. Which of the following forms of energy depends on energy from the sun? Select all correct answers a. fossil fuel energy b. nuclear fission c. geothermal energy d. wind energy 13. Which of the following statements about photovoltaic cells is true? Select all correct answers. a. They are not yet commercially viable. hey use mirrors to focus sunlight on a tube carrying a heat transfer fluid. c. They produce electricity directly from sunlight. d. They do not require connection to the electric grid.Explanation / Answer
9) Option b is correct.
High yield crop varieties need fewer soil nutrients compared to their wild ancestors.
Because the introduction and broad adoption of scientific agriculture since the mid-19th century contributed to crop yield growth in the United States.
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