6660
While today a generally flat and open landscape , in the Iron Age it was covered by bog , quicksand , and ponds , surround by dense woodlands of birch , willow , hazel and alder while higher ground was covered by oak and ash .
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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:
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