Why do Revolutions occur?

The nineteenth century was an era of great inventions in the united states. look at the list of inventions below and order them from most to least important (in your opinion). then explain why you ranked the top three inventions as most important. 1834: refrigerator invented by jacob perkins 1837: morse code invented by samuel morse 1853: elevator invented by elisha graves otis 1873: typewriter invented by christopher latham sholes 1876: telephone invented by alexander graham bell 1877: gramophone invented by thomas edison 1879: light bulb invented by thomas edison 1886: dishwasher invented by josephine cochran

Who did the first work in creating vaccines

56: 58 the assembly line was a system through which items were mass-produced in a flow.