12491
Dr. Chung suggests that fitness should begin when young , and those who start very late should stick to swimming , fast walking , and exercise bikes , which are of moderate intensity .
 Chung
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: date, organization, person, geographical social political, national religious political, facility, cardinal, location, work of art, law, event, product, ordinal, percent, time, quantity, money, language 
Text: {0} 
Answer:
 Chung