Right ok so I'm not sure how much you know about this stuff but let's say there is a map you like and you want to use it in Inkscape. Go to the view source and copy the HTML between the svg and /svg. Open up a notepad document and paste the HTML into the document and save it. When you save it make sure that the type of document is 'all files' and not a '.txt' and when you type in the name of the file make sure it ends in .svg e.g 'rivermap.svg' Now it is saved as an svg file it can be opened up in Inkscape.
I got the 9 most guessed ones, and I knew Ob aswell, not sure I have ever heard of any of the others though. I did guess Paraguay, Uruguay and Rio grande, which all flow into it, and rio dela Plata.
Nice quiz by the way