Why does author point out that "Indian grass, Canada wild rye, and native big bluestem all grew higher than a person"? A. To provide a reason why people from the eastern woodlands of the United States were impressed when they saw the prairie B. To identify an obstacles to the development of the railroad lines fanning out from Chicago C. To explain why the transformation of the prairies by commercial agriculture was so remarkable D. To provide evidence supporting the claim that the prairies had fertile, deep black soil