I think c, a and b just learn and study about what was built before
Farewell Address by Washington--this address urged the nation to avoid alliances and getting involved in affairs not our own. This set the tone for isolationism.
Monroe Doctrine--this foreign policy stated the US would protect the Western Hemisphere from European involvement and implied the US would stay out of European affairs.
The Treaty of Versailles and League of Nations would involve the US in world affairs and bring European issues to the doorstep of the US.
The correct answer is: frontier farming became easier because there were new tools that helped break the soil faster. However, even though there were many useful tools for farming, it was also difficult for people to get a job since the machines were taking their places.
For example, there were new machines such as farming with windmills, steel plows and reaping machines which made harvesting quick and easy.
Nevertheless, it was hard for farmers to pay for these tools and put them in debts. They dealt with economic problems as crop prices dropped and their debts grew.
The Apollo-Soyuz Test Project was a joint United States-U.S.S.R. venture to live and work together on a space platform in orbit.
The New Deal reform that helped labor unions win the right to represent workers was the "(3) passage of the National Labor Relations <span>(Wagner) Act" but there were other things as well. </span>
