61987
Guided or unguided concrete bombs may also be used for training pilot s and ground personnel , due to the advantages of cost ( no explosives or fusing ) , point of impact determination , minimised bombing range damage and safety .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None