Hey MB - thanks for the question!
I believe this mostly comes down to a misreading.
"Unrest" in (B) simply means discord in the region, something we would surely expect to find a fair amount of in an empire in decline. It's not a cause of the decline, but a symptom. A sign that things truly are beginning to fall apart.
So when (B) says that the areas of greatest climatic instability experienced no more unrest than other areas, it's actually
weakening the argument that climatic fluctuations were the cause of problems: the places where the climate was least stable didn't see any greater problems than more climatically-serene regions.
Instead, we want to show a stronger connection between climate and Roman empire success/failure. That the ups and downs of the empire may indeed be tied to the weather.
(D) gives us that connection by saying when the climate was favorable for agriculture (unlike the time period in the stimulus), the Roman empire thrived! The idea of good climate/crops
empire success makes the notion of
bad climate/crops
empire collapse more likely.
Note: (D) is a long way from proving anything in the stimulus. It simply shows a tighter link between weather/crops and the success of the empire, which bolsters the claim that poor weather could hamper that success.
Jon Denning
PowerScore Test Preparation
Follow me on Twitter at
https://twitter.com/jonmdenning
My LSAT Articles:
http://blog.powerscore.com/lsat/author/jon-denning