19980
Initially sensors were optical and acoustic devices developed during World War I and continued into the 1930 s , but were quickly superseded by radar , which in turn was supplemented by optronics in the 1980 s .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None