Task: Question Generation
Input (English): #1 return river 
#2 return mali 
#3 return niger 
#4 return nigeria 
#5 return #1 that flows through #2 
#6 return #1 that flows through #3 
#7 return #1 that flows through #4 
#8 return #1 in  both  #5 and #6 
#9 return #1 in  both  #8 and #7
Output (English): what river flows through mali niger and nigeria?