According to historian Sean Wilentz, speaking in the PBS conversation about blackface ministrelsy, blackface entertainment became popular in the 1830s because that's when ________.
1) The sewing machine and steel plow were invented, freeing workers' time for entertainment
2) Wine began to be shipped to America in bottles with cork stoppers, which white performers used to blacken their faces
3) Issues around slavery and abolition began to heat up in the North and the South
4) No answer text provided