1) International relations encompass the study of relationships between nations, including diplomacy, treaties, and foreign policy. It examines the interactions and dynamics among different countries in the global arena.

2) The word "umbrella" contains three vowels: U, E, and A.

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

4) The Mona Lisa, painted by Leonardo da Vinci, is one of the most famous and valuable artworks in the world.