Task: Question Generation
Input (English): #1 return directors 
#2 return director NULL 
#3 return #1 besides #2 
#4 return movies that  #3 made 
#5 return the  number of  #4 for each #3 
#6 return #3 where #5 is  one 
#7 return the  names of #6
Output (English): What are the names of the directors who made exactly one movie excluding director NULL?