The correct answer is option 1, the Maastricht Treaty. The Maastricht Treaty is the treaty that laid the groundwork for the establishment of the European Union (EU). It was signed in Maastricht, Netherlands, in 1992.

Option 2, the Treaty of Paris, is a significant treaty in European history, but it does not directly relate to the formation of the EU. The Treaty of Paris, signed in 1951, established the European Coal and Steel Community (ECSC), which aimed to integrate the coal and steel industries of European countries to promote economic cooperation.

Option 3, the Treaty of Rome, is also an important treaty but is not the basis of the EU. The Treaty of Rome, signed in 1957, established the European Economic Community (EEC), which focused on creating a common market among the member states.

Option 4, the Treaty of Lisbon, is a more recent treaty in the history of the EU. It was signed in 2007 and aimed to streamline and improve the institutional functioning of the EU. While it made several amendments to the existing treaties, it did not establish the EU or serve as its basis.

Therefore, the correct answer remains option 1, the Maastricht