Obviously the 9 people who voted for Rio have never been anywhere near it....
If it must be held in SA then Buenos Aires is the only choice.
Santiago, Chile could host it, too, and Rio has PanAm experience, but I do tend to agree that the games would be better in BsAs (or Santiago) than one of the Brazilian cities.
Santiago is another city that could hold the games, but I'm not sure if the infrastructure is there. There would definitely have to be a lot of work done that wouldn't necessarily need to be done in BA. Kind of like the work that was needed in Salt Lake or Atlanta
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