1) The European Union (EU) is a supranational organization comprising 27 member states that cooperate on various issues, including trade, economic integration, and common policies, while preserving individual national sovereignty.

2) The invention of the printing press by Johannes Gutenberg in the 15th century revolutionized the spread of knowledge and played a key role in the Renaissance.

3) The Federal Reserve System, often referred to as the Fed, is the central banking system of the United States.

4) The Earth's core is hotter than the surface of the Sun.