I'm pretty sure that the answer to this question is letter A.
Probably rivers and water sources, because you need water to farm, and the water by rivers is rich and the soil is good. So yea the rivers and other water sources would be the main thing.
Answer:
Subcontinent is a large landmass, smaller than a continent.
Explanation:
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The State of the Union, though valuable, is not completely necessary. Choose D.