Detailed Instructions: In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Q: This river contains Csepel Island and Belene Island, and the city of Sulina lies at its mouth. This river receives the Naab and Regen in Regensburg, and its primary sources are the Breg and Brigach Rivers. The Devin Castle dominates the landscape of the area where this river receives the Morava. This river receives the Tisza and Sava Rivers, and in 2010(*) toxic sludge from Hungary contaminated its waters. Rising in the Black Forest, this is, for 10 points, what river that passes through Belgrade and Budapest before emptying into the Black Sea
A:
Social Science