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Sionidis also participated in the Battle of Skra-di-Legen during World War I , and worked as a secret agent of Third Army Corps behind enemy lines , in the area of Strumica .
 Sionidis, Third Army Corps, Strumica
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Sionidis, Third Army Corps, Strumica