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

2) Serena Williams is an American professional tennis player widely regarded as one of the greatest athletes in the sport. She has won numerous Grand Slam titles and Olympic gold medals and has become an influential figure both on and off the tennis court.

3) The United States operates under a two-party system, with the Democratic Party and the Republican Party being the two major political parties that compete in elections and shape the country's political landscape.

4) The world's first insurance policy was issued in 1347 in Genoa, Italy. It insured against the risk of maritime trade.