Excellent quiz. I knew 16/17 and by randomly guessing large countries soon got the 17th with two and a half minutes to spare. Should you consider reducing the time limit - unless you are happy with an average score rate of 15/17.
Rivers really amaze me. I didn't know the Brahmaputra (or in other cultures: Yarlung Tsangpo/Siang/Dihang River/Luit) so I looked it up and the course of the river is very interesting. The wide river on the very high plains changing into a thin (probably deep and rapid) river cutting through giant mountains ending into the great delta of Bangladesh. Everywhere having huge impact on culture, agriculture, economy, religion, transport, and so on...
Please, change Oder for Odra. In Germany the river only touches the border. Both Poles and Czechs calls it "Odra" and that is a majority. I actually missed that one, though I am Czech, because I had no idea, what Oder means.
And that's just one of them...