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In 1913 , the Russian Empire also began the construction of the four-ship , which were designed for service in the Baltic Sea .
 Russian Empire, Baltic Sea
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 Russian Empire, Baltic Sea