65871
It contained major changes that included the Wright R-1510-98 radial engine , single-leg cantilever main landing-gear unit s , a slight increase in the interplane gap , metal - rather than fabric-covered control surfaces , and armament based on two fixed forward-firing machine gun s supplemented by a hardpoint under the fuselage for the carriage of a bomb , or an auxiliary fuel tank .
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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