1764
He also formulated a theory of gradual climate change , after his observation of ancient petrified bamboos found in a preserved state underground near Yanzhou ( modern Yan'an ) , in the dry northern climate of Shaanxi province .
 location: Yanzhou; location: Yan'an; location: Shaanxi
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 location: Yanzhou; location: Yan'an; location: Shaanxi