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Southdown Road Skew Bridge is a ribbed skew arch railway bridge , which carries the Midland Main Line across Southdown Road in Harpenden , Hertfordshire .
 Midland, Harpenden, Hertfordshire
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Midland, Harpenden, Hertfordshire