9734
Just 12 production models were built , as the aircraft was obsolescent at the time it was brought into service in 1935 , and only eight were serviceable at the time of the German-led Axis invasion of Yugoslavia in April 1941 .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities:  
Answer:
 None