1) The invention of the printing press by Johannes Gutenberg in the 15th century revolutionized the spread of knowledge and played a key role in the Renaissance.

2) Cows have best friends and can become stressed if they are separated.

3) The Great Barrier Reef in Australia is the largest coral reef system in the world and is visible from space.

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.