It would be "rope" that led to the closing of the open range, as farmers started to close off their land to other people and cattle. Barbed wire was not generally used.
Marginal costs. Keep in mind that marginal means on the edge of something, so the cost of producing one more unit would be on the edge. Hope this explanation helps.
I was hoping that some options would be given to choose the right answer. As there are no options given in the question, so this question has to be answered by research or knowledge. I hope the answer comes to your help. Oversight and public education are examples of non legislative functions of the Congress.
