What would a historian need to examine most closely for bias?

Look at this photograph taken during the battle of guadalcanal

Which of the following is an example of the pull factor known as economic migration? a. better educational opportunities pulling people towards a new country b. mexican laborers entering the us to work in agricultural jobs c. joining family members that are already in a new country d. crop failures driving people away from their country i am unsure on this question, i was thinking b? but i could be wrong.

Which of the following statements about the economic consequences of the civil war is not accurate. a. inflation caused prices to rise by 80% in the north. b. because southern farms cannot process enough food for everyone in the south the union navy allowed food shipments from britain. c. to pay for all of the food supplies and arrangements that were necessary for the union army congress instituted an income tax. d. business boomed in the north as factories and farms always had a market for their products.