I came across the below in the free MGMAT CAT and wouldn't mind your view on it.
To this day, researchers and theorists debate whether
bubonic plague caused The Black Death, a pandemic that swept the world in the middle of the fourteenth century.
whether or not
as to whether
The official answer is (a) for it's concision, but I put (b) on the idea that 'whether or not' is an idiom. So what I'm trying to get my head around is in situations where concision can occur without prejudicing meaning, or an idiom if offered, what trumps what?
In the study cave!