challenge: Who did Al-Altan marry as part of Genghis Khan's policy of forming alliances through marriage?
  
  A. Barchuk, the ruler of the Uighur people to the southwest
  B. A ruler of the Tanguts to the southeast
  C. A king of the Jin dynasty to the south
  D. A leader of the Khwarezmid Empire to the west
  Answer: 