51313
The field began to flourish in 1971 when the Stephen Cook and Leonid Levin proved the existence of practically relevant problems that are NP-complete .
 person: Stephen Cook; person: Leonid Levin
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: Stephen Cook, Leonid Levin 
Answer:
 person: Stephen Cook; person: Leonid Levin