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Repeat photography of the glaciers , such as the pictures taken of Grinnell Glacier between 1938 and 2009 as shown , help to provide visual confirmation of the extent of glacier retreat .
 Grinnell Glacier
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Grinnell Glacier