1) The Beatles hold the record for the most number-one hits on the Billboard Hot 100 chart, with 20 songs reaching the top spot.

2) The process of nuclear fusion powers the sun and other stars, fusing hydrogen atoms together to form helium and releasing vast amounts of energy in the process.

3) The assassination of Archduke Franz Ferdinand of Austria in 1914 triggered the start of World War I.

4) Rihanna, born Robyn Rihanna Fenty, is a Barbadian singer, actress, and businesswoman. She has achieved great success in the music industry with hits like "Umbrella," "Diamonds," and "Work," and has also ventured into the worlds of fashion and cosmetics with her brands.