1) The blue whale is the largest animal to have ever existed, with an average length of about 82 feet (25 meters).

2) The Amazon rainforest produces more than 20% of the world's oxygen.

3) The concept of self-driving cars, or autonomous vehicles, is being actively developed by companies such as Tesla, Google (Waymo), and Uber.

4) Serena Williams, an American tennis player, has won a total of 23 Grand Slam singles titles, making her one of the most successful players in the history of the sport.