(D)The development of stone tools, because the neolithic age has to do with the development of human tools.
It was a result of the cooperation between the public and the private sector. The private sector owners built things like railroads and public roads so they wanted to get money back through tolls and turnpikes. In return, they would pay taxes for money obtained this way and the states enjoyed this money and wasn't bothered by what was happening.
WW2 set the economy into a big progression era after the the Great Drepression. Companies were hiring worker and producing goods to support the soldiers. When the soldiers returned from war, the women left the factories and started families. This opened jobs for the returning soldiers and launched a big population boom “the baby boom” which ultimately resulted in more consumerism.
