In many human cultures, agriculture is practiced as an extractive industry, in which the nutrition in the soil is sucked out by the repeated growing of crops, and soils are routinely degraded throughout the world.
The conversion of land to agricultural purposes alters the entire ecosystem, and the resulting impact on soil structure and fertility, quality and quantity of both surface and groundwater, and the biodiversity of both terrestrial and aquatic communities diminishes present and future productivity. Crop rotation and the application of livestock manure help to reduce soil erosion, but in some parts of the world the land is robbed of even cow dung by the need of growing populations for something to burn as fuel for cooking and staying warm.
The eroded soil has to go somewhere, of course, and its usual destinations are riverbeds and lake bottoms, where it often causes secondary problems by choking reservoirs.
In some parts of the world, the land is robbed of even cow-dung for:
The passage says the land is robbed of even cow dung for something to burn as fuel for cooking and for staying warm.
So the two uses are fuel and staying warm, matching the fourth option.
Growing populations need cheap fuel, and dried cow dung serves as that fuel.
Diverting dung to burning removes it from its role as manure that reduces soil erosion.
The other options add uses like medicine or rituals that the passage does not mention.
The answer comes directly from the sentence about burning dung for cooking and warmth.
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