challenge: What is the relationship between the Hellinger distance H(P,Q) and the total variation distance δ(P,Q)?
  
  A. They are related, but the exact relationship is not specified
  B. They are unrelated measures of distance between probability distributions
  C. The total variation distance is a special case of the Hellinger distance
  D. The Hellinger distance is a special case of the total variation distance
  Answer: 