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The issue of system response to users has been extensively studied by the natural language generation community , though rarely in the context of dialog systems .
 system response, natural language generation community; natural language generation community, dialog systems
Please list all entity pairs containing a certain relationship in the given options.Output format is "word1, word2; word3, word4". 
Option: conjunction, feature of, hyponym of, used for, part of, compare, evaluate for 
Text: {0} 
Answer:
 system response, natural language generation community; natural language generation community, dialog systems