Why is grain production in the Great Plains considered largely unsustainable?
A) Competition with cattle ranching is resulting in a decline in crop production.
B) More and more people are becoming gluten intolerant, so there will be less and less demand for wheat, barley, and rye.
C) The Ogallala aquifer is being depleted for irrigation water.
D) The energetics of crop production in the Great Plains are such that more energy is needed to grow the crops than can be gotten from the crops.
E) So many pesticides are needed for grain production that streams in the Great Plains are becoming dead zones.
Answer: C
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