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These kites also fall into a category of foils called " closed-cell inflatables " , meaning that the ram-air inlets on the leading edge of the kite are normally closed by flaps that act as one-way valves to maintain internal air pressure .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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