Answer:
Oder, Danube, Rhine
Step-by-step explanation:
The Rhine, Elbe, and Weser are the rivers that are most significant (from an economic standpoint). Ems and Donau, in lesser portions.
Bremerhaven and Bremen on the Weser, Duisburg (and Rotterdam in the Netherlands) on the Rhine, and Hamburg on the Elbe all have deepwater harbors. From there, smaller ships may transport bulk materials through Germany's (very vast) network of shipping channels, tributaries, and rivers.
Ships may utilize the Rhine itself all the way up to Basel, Switzerland. Additionally, it has access to the Danube via the Main via the Rhein-Main-Donau-Kanal.
Thanks,
Eddie