The comma vs. period standard jumps between the European and American usage throughout the questions: 17,53% (EU), 52.500 people (EU), 9.5 million people (NA), 20,310 feet (NA) Regarding American punctuation, periods are used to indicate decimals (10.5 million dollars / 13.8%) while commas are used to separate places in large numbers (52,500 people / 10,438 feet).
And the question "Who was the biggest rival of the US during the XIX century?" is incorrect. It should be the XX Century (20th Century = 1900s) as the Soviet Union did not yet exist in the 19th Century (1800s). Generally, Americans wouldn't write centuries in the Roman Numeral form either, but it's still understandable to most. https://en.wikipedia.org/wiki/Soviet_Union
Regarding American punctuation, periods are used to indicate decimals (10.5 million dollars / 13.8%) while commas are used to separate places in large numbers (52,500 people / 10,438 feet).
And the question "Who was the biggest rival of the US during the XIX century?" is incorrect. It should be the XX Century (20th Century = 1900s) as the Soviet Union did not yet exist in the 19th Century (1800s). Generally, Americans wouldn't write centuries in the Roman Numeral form either, but it's still understandable to most.
https://en.wikipedia.org/wiki/Soviet_Union