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In Berlin , the S-Bahn systems arguably fulfill all considerations of a true metro system ( despite the existence of U-Bahns as well ) – the trains run on tracks that are entirely separated from other trains , there are short distances between stations , the trains are high frequency , and use tunnels but do run a bit further out from the city centre compared with U-Bahn .
 Berlin, S-Bahn, U-Bahns, U-Bahn
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Berlin, S-Bahn, U-Bahns, U-Bahn