challenge: Why did Stalin transfer troops from Siberia and the Far East to the Moscow front?
  
  A. Because the Red Army needed to defend against a potential Soviet rebellion
  B. Because Richard Sorge informed him that Imperial Japan had no plans to invade the USSR in the near future
  C. Because the Wehrmacht's offensive had been stopped and the Red Army was on the counterattack
  D. Because Imperial Japan had launched a surprise attack on the USSR
  Answer: 