C - Guns
While illegal to trade ivory, Africa traded the tusks of African elephants, is number 5 in the world for gold, and different tribes would capture members of warring tribes and sell them in the slave trade.
Kansas topeka is one of your answers
1.) The group that benefited the most from barb wire was the farmers. The correct answer is D.
2.) A major challenge facing the builders of the transcontinental railroad was crossing the Sierra Nevada mountains. The correct answer is D.
I would say your answer is A. B wouldn't be feasible due to the South and their bias towards African Americans, C is also incorrect, because they had no choice but to join after the war, and D while accurate doesn't describe the whole picture.
mine would be a farmer or trader