4621
At the same time , it says , China will grapple with problems associated with a rapidly aging population and lack of an extensive social security system .
 China, a rapidly aging population
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: geographical social political, organization, person, location, facility, vehicle, weapon 
Text: {0} 
Answer:
 China, a rapidly aging population