[填空题]

• A. industrially polluted soils
• B. rock and soil chemistry
• C. naturally polluted soils
• D. the pathways of metals into the food chain
• E. the element of iodine
• F. the persistence of heavy metals

It is extremely necessary to study the long-term effects caused by living on ______.

[填空题]

• A. industrially polluted soils
• B. rock and soil chemistry
• C. naturally polluted soils
• D. the pathways of metals into the food chain
• E. the element of iodine
• F. the persistence of heavy metals

Some serious diseases are connected with deficiency of ______.

[填空题]A. industrially polluted soils
B. rock and soil chemistry
C. naturally polluted soils
D. the pathways of metals into the food chain
E. the element of iodine
F. the persistence of heavy metals

Some serious diseases are connected with deficiency of ______.

[简答题]
1 Soil is a renewable resource, but only on a very long time scale, as it takes hundreds or thousands of years for the natural processes of erosion, organic decay, and accumulation to create soils．Soil quality and the potential to produce crops can vary enormously from region to region and among various soil types．
2 One important factor affecting the productivity of soils ever time is agriculture．Top-quality lands are brought into production earlier because of their higher potential to produce food．As more and more land has been brought under agricultural production, the average quality of land has decreased, reducing potential productivity per hectare．Crops deplete soil fertility by consuming nutrients, and this eventually reduces crop yields．Poor management practices lead to soil compaction and soil pollution as well as loss of soil cover．Without proper management and the constant addition of nutrients and e

[单项选择]
1 Soil is a renewable resource, but only on a very long time scale, as it takes hundreds or thousands of years for the natural processes of erosion, organic decay, and accumulation to create soils．Soil quality and the potential to produce crops can vary enormously from region to region and among various soil types．
2 One important factor affecting the productivity of soils ever time is agriculture．Top-quality lands are brought into production earlier because of their higher potential to produce food．As more and more land has been brought under agricultural production, the average quality of land has decreased, reducing potential productivity per hectare．Crops deplete soil fertility by consuming nutrients, and this eventually reduces crop yields．Poor management practices lead to soil compaction and soil pollution as well as loss of soil cover．Without proper management and the constant addition of nutrients and energ
A. Soils with high salt concentrations are destructive to crop plants．
B. Salinization can lead to soil compaction or to LOSS of soil cover．
C. Excessive amounts of water are required to prevent salinization．
D. Adding salt to fertilizer raises the operating costs of agriculture．