Question: What duo in the Simpsons episode "Gump Roast" usually appear in the Treehouse of Horror episodes? 
Sentence (from "Treehouse of Horror XIII"): It is the second Treehouse of Horror to have a zombie related segment, and the last Treehouse of Horror to have three separate writers credited for writing three stories (starting with "Treehouse of Horror XIV", only one writer is credited for writing the three stories).
Relevant evidence: No