The human activities that cause the desertification in the Sahel are the overfarming and grazing of large herds.
What is desertification?
Desertification is defined as a form of dryland land degradation in which biological production is suffered as a result of natural processes or human activity, causing productive regions to become increasingly arid.
The Sahel, however, has been suffering from a severe drought since the late 1960s.
During a natural period of drought, desertification occurs when land surfaces are modified by human activities such as overgrazing, deforestation, surface land mining, and poor irrigation systems.
Overfarming and grazing huge herds are two human practices that contribute to desertification in the Sahel.
Therefore, option D is correct.
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