The correct answer is "A".
The Domino Theory was developed in 1950 in the US administration. It proposed the idea that if one country in a region was governed by a left-wing power which shared communist beliefs, neighbor countries will follow suit. This led the United States to get involved in numerous armed conflicts around the world, such as the Korean War, in order to prevent the spread of Communism.
They created the number system and discovered that the earth was round by studying eclipses.
Hope this helps.
Industrialization moved the economy away from agriculture.
They allowed for travel against a rivers current Hope this helps! ;D
