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Apart from the new engines , the R. VII also received extensive modifications while still at the factory , including overall strengthening to take the greater weight of the heavier Mercedes engines , as well as changes to the fuel tanks , propellers , and undercarriage .
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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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