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During the 10th century AD , the people of Igbo-Ukwu , near the Niger Delta , buried their leaders with elephant tusks .
 Igbo-Ukwu, Niger Delta
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Igbo-Ukwu, Niger Delta