37720
Like most of Blackburn 's aircraft of the time , the fuselage was built up around four steel longeron s ; it was duralumin covered from nose to just aft of the rear observer/gunner 's cockpit , the rest fabric covered .
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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:
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