As a result of improved farming technologies and techniques, Western settlers A. were able to employ more Plains Indians. B. demanded more land from the Plains Indians. C. learned to peacefully coexist with the Plains Indians. D. sold more manufactured goods to Plains Indians.

B. demanded more land from the Plains Indians.

Explanation:

With better agricultural techniques and technologies, the need for Europeans to expand agricultural frontiers and produce agricultural products in greater quantities has grown. This meant that the Europeans needed more land to be able to establish their agricultural crops and produce on a large scale, but the lands were occupied by the Indians and as you may already know, the Indians had no value to the Europeans, so In order to be able to produce more agricultural products, Europeans demanded (and took) more land from the lowland Indians.

I think the best answer is A