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During reconstruction , the Eastern end of the tunnel was opened out and was then supported by two brick-built flying arch es The banks of the cutting were so unstable that even during this opening-out work , timber horseshoe shoring was required .
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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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