challenge: What was notable about the length of Vitagraph's 1910 production of Uncle Tom's Cabin?
  
  A. It was a two-reeler, roughly 30 minutes long
  B. It was a five-reeler, over an hour long
  C. It was a standard one-reeler, approximately 15 minutes long
  D. It was the first three-reeler, an innovation in film length at the time
  Answer: 