Which of these statements about social mobility in the u. s. is true?

What was the name of the theory that said that if one country in a region fell to communism, others would surely follow? 1) domino theory 2) arms race 3) brinkmanship 4) containment theory

Predict how the transcontinental railroad will make a difference in the civil war. now, research the inventions of the 19th century. tell what other inventions of the 19th century will change the way people see and remember the war? why?

Based on this expert how did banksy counteract this characterization as a "sell out"?