1) The word "oxygen" contains two vowels: O and E.

2) The highest-grossing film of all time is "Avengers: Endgame," which has earned over $2.79 billion at the global box office.

3) 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.

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