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In retrospect the name change was unfortunate , not only because the Greek roots alone do not reveal the cathode 's function any more , but more importantly because , as we now know , the Earth 's magnetic field direction on which the " cathode " term is based is subject to reversals whereas the current direction convention on which the " exode " term was based has no reason to change in the future .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities:  
Answer:
 None