challenge: What was the cause of the sinking of German submarine U-3508 on 4 March 1945?
  
  A. Mechanical failure due to a faulty engine
  B. Sunk by a German torpedo during a training exercise
  C. Allied bombing raid by US Eighth Air Force B-24 Liberator bombers on Wilhelmshaven
  D. Collision with a British naval ship
  Answer: 