35582
Some methods of fertility awareness , such as the Creighton model and the Billings method involve estimating a woman 's periods of fertility and infertility by observing physiological changes in her body .
 person: Creighton; person: Billings
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: Creighton, Billings 
Answer:
 person: Creighton; person: Billings