1) The musical "The Phantom of the Opera" has been running in London's West End since 1986, making it the longest-running musical in history.

2) Bats are the only mammals capable of sustained flight.

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

4) The Dow Jones Industrial Average (DJIA) is a stock market index that tracks the performance of 30 large, publicly owned companies in the United States.