I couldn't get past St. Petersburg and Yekaterinburg and thought it was a trick question. I blame the fact that it's early and I haven't had my coffee yet.
I would specify what the country of origin for the borscht question since each country has a different main ingredient... For instance, in Poland the main ingredient is mushrooms
Sure, it’s not the great question, generally speaking. ABBA isn’t really all that disco. But then neither are The BeeGees. They did a disco movie’s soundtrack, and they got labelled as disco by people unfamiliar with their other works. A better way to ask this would be, “What band has the best-selling disco album of all time?”