Answer:
D. German and Scandinavian immigrants
Step-by-step explanation:
In the period between 1820 and 1850, the US was still not fully formed as we now know it. The western frontier was actually where the central part of the US is in the present, which is also the most fertile part of the country. There were several policies by the government to convince the people to start moving toward the west, one of which were granting large pieces of land for free or for very small amounts. In this period there were lot of immigrants coming from the German states and Scandinavia as these countries were poor and in terrible conditions, sot hey were looking for better life. Once they saw the opportunity to have their own large lands for pretty much nothing and become farmers, they took the chance and settled on the western frontier.