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Located at the confluence of the Rhine river and its tributary the Ruhr river , it lies in the west of the Ruhr urban area , Germany 's largest , of which it is the third-largest city after Dortmund and Essen .
 Rhine, Ruhr, Ruhr, Germany, Dortmund, Essen
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Rhine, Ruhr, Ruhr, Germany, Dortmund, Essen