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Canal building progressed steadily in Germany in the 17th and 18th centuries with three great rivers , the Elbe , Oder and Weser being linked by canals .
 Germany, Elbe, Oder, Weser
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Germany, Elbe, Oder, Weser