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Due to sumps , the stream of the Rak is very difficult to follow and was explored by divers only in 1974 , when the majority of the cave was discovered in the course of a rescue expedition , and in August 2012 .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None