question: what is africa's fourth largest river?
#1 return africa 
#2 return rivers of #1 
#3 return the  largest of #2 
#4 return #2 besides  #3 
#5 return the  largest of #4 
#6 return #2 besides  #5 
#7 return the  largest of #6 
#8 return #2 besides  #7 
#9 return the  largest of #8