Answer:
<em><u>D. fencing off the plains with barbed wire.</u></em>
Explanation:
The great plains were fenced off with barbed wire, and I <em>think</em> it was mostly done in modern-day Texas, Oklahoma, Kansas, Nebraska, and the Dakotas.
<em>Hope this helps! Feel free to give me Brainliest if you feel this helped. :)</em>