sentences:  Me advokos doktoro e lu decidez quon me agos
  
  Since I don't know whether a male or female doctor will come, I cannot use here il(u) or el(u).And I definitely cannot use ol(u) since I know for a fact that the doctor who comes is going to be a human being.Now if instead of "a" doctor, I decided to call "my" doctor (therefore, knowing whether it will be a man or a woman), I could use any of the following