Task: Question Generation
Input (English): #1 return Goryeo-Mongol assault first began 
#2 return when  was  #1 
#3 return the  Mongols directly control Tamna 
#4 return when  was  #3 
#5 return difference of #4 and  #2 in  years
Output (English): For how many years after the Goryeo-Mongol assault first began did the Mongols directly control Tamna?