Which of the following statements are correct regarding the history of the U.S. personal income tax?
1) The 16th Amendment to the U.S. Constitution gives the government the power to levy an income tax.
2) The U.S. personal income tax was first introduced in the early 20th century.
3) The U.S. personal income tax is based on a progressive tax system.
4) The U.S. personal income tax is the primary source of revenue for the federal government.