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 windshield wipers were invented by a woman named Mary Anderson in 1903.

3) A newborn kangaroo is about 1 inch (2.5 centimeters) long and weighs less than a gram.

4) The Earth's core is primarily composed of iron and nickel and is as hot as the surface of the sun.