1) The word "piano" contains three vowels: I, A, and O.

2) The largest living structure on Earth is the Great Barrier Reef, spanning over 2,300 kilometers (1,400 miles) along the coast of Australia.

3) The Industrial Revolution led to significant urbanization, as people migrated from rural areas to cities in search of employment in factories.

4) The Mongol Empire, under the leadership of Genghis Khan, became the largest contiguous empire in history, spanning from Asia to Europe.