challenge: What is the premise of Philip José Farmer's alternate history short story 'Sail On! Sail On!'?
  
  A. The Earth is round, but Christopher Columbus believes it is flat and sets out to prove it.
  B. Christopher Columbus sets out to find a new route to the New World, but discovers a hidden continent.
  C. The story is set in a world where the Black Death never occurred, and the population of Europe has grown exponentially.
  D. In an alternate 1492, the Earth is flat, and Christopher Columbus sets out to find a shortened route to China and South-East Asia.
  Answer: 