The central economic problem that all humans face is A shortage
B. scarcity
C. opportunity cost
D. the factors of production

the answer is "d"

(context) if you were to travel to the middle east and go into peoples homes there would be like 4 generations in there

(more context) i'm pretty sure in the middle east they take loyalty and family bonds very serious

(last bit of context) i'm also positive that extended families are most commonly found in urban areas

the first phase of the government’s plan for settlement was building the transcontinental railroad. the railroad provided a way to bring settlers and manufactured goods west and ship their agricultural and mining produce east. the transcontinental railroad was an essential artery for rapid development of the frontier.

the second phase of the government’s plan was a liberal land distribution policy that made it possible for many people to homestead. with these two key elements—transportation and cheap land—the government rapidly achieved its goal of persuading people to move west, settle on farms, and push back the frontier.