No clue. I must've guessed on that one. I do remember that this passage came up.
I was thinking it could've been node in relation to closed pipe. In Kaplan book, for the closed pipe, it says that closed end of the pipe represents node or something. I figured same thing can be said about the wall....
Did the question ahd four choices? like
Node/Constructive
Node/Destructive
AntiNode/Contructive
Antinode/destructive?