Which scenario is an example of a referendum?

1.Citizens in Wisconsin vote on an amendment to the state constitution passed by the legislature that would grant certain rights to crime victims.
2.Citizens in Philadelphia, Pennsylvania, propose a law that would prevent the police from using “stop and frisk” measures.
3.Citizens in Florida speak out against a new law voted on by the state legislature that would reduce funding for the state highway patrol.
4.Citizens in King County, Washington, propose a new law that would require members of the county sheriff’s department to wear body cameras.