1) The Danube River, flowing through ten countries in Central and Eastern Europe, is the second-longest river in Europe. It has played a significant role in the cultural and economic development of the regions it traverses and is a popular waterway for river cruises.

2) The Mona Lisa, painted by Leonardo da Vinci, is one of the most famous and valuable artworks in the world.

3) The invention of the transistor by Bell Laboratories in 1947 revolutionized electronics and paved the way for the development of smaller, more efficient electronic devices.

4) The world's first credit card was introduced in 1950 by Diners Club.