challenge: What is overstemming in the context of stemming algorithms?
  
  A. When a single inflected word is stemmed to multiple roots
  B. When two inflected words are not stemmed to the same root, but should have been
  C. When a single inflected word is not stemmed at all
  D. When two separate inflected words are stemmed to the same root, but should not have been
  Answer: 