I'm going to infer you are talking about Irony. It would be situational irony.
Answer:
It was an execution stand.
Explanation:
Based on the context of expression used in the Hangman poem such as "capping sill of the courthouse door" it portrays a court house scene.
Therefore, the scaffold changed in size when it fine to execute or hang the two persons (victims) sentence. This hanging would have warranted increasing the height of the scaffold.
Wrong: I think it is D. Comparison
Correct : A. Definition
