337547
Students , referred to as Replacement Pilots or Replacement Weapon Systems Officer s are either newly winged aviators ( Category I ) , aviators transitioning from one type aircraft to another ( Category II ) , or aviators returning to the cockpit after a period of non-flying ( Category III ) .
 Replacement, Replacement
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Replacement, Replacement