The best answer is D. The Truman doctrine helped to prevent the spread of Communism past the already established boundaries after WWII. The United States would give economic assistance to countries in need so they did not have to turn to a Communist country for assistance. It wasn't just for third world countries, but any independent country in need that the United States felt might have Communist assistance and allow that ideology to expand.
The acient sumerian kingdoms built their most important temples outside of the main city
Slaves, because when the slaves came over to the U.S.A. people among the states would fight and that could cause them to split which added more and more states.
The answer in this question is Incas. The Inca empire or Incan empire is the largest empire in pre- Columbian American and also it is the early civilization that had a well organized unified empire with an elaborated system of roads covering more than 10,000 miles.
"The speech by President Reagan at the Berlin Wall" was considered the end of the Cold War, since the Berlin Wall was considered the most physically divisive element of the war.