Answer choice B, that "there are terraces on farmland in Dooney County which were built to prevent soil erosion" is necessary to the author's argument because, without assuming this statement, the conclusion does not follow. You need a bridge that makes the non-flatness of Dooney County inferable from the fact of terraces there. For the terraces to show that the County isn't flat, they have to be built to prevent erosion as one of the premises states "farmers whose land is flat do not build terraces to prevent erosion." Therefore, farmers whose land is NOT flat, build terraces to prevent erosion. In other words, farmers in Dooney County built terraces to prevent erosion.

Hi, I'd love to join!!

Hi, I'd also love to join!!

I knew the answer from taking a Shakespeare class in college :)