The most favorable locations for the growth of glaciers, rather than being the cold, dry polar regions, would be instead the cool, moist middle latitudes, where there is abundant precipitation and where it is cold enough to allow some snow to accumulate year by year.
(A) glaciers, rather than being the cold, dry polar regions, would be instead the cool, moist middle latitudes( awkward,being,would be instead)
(B) glaciers are not the cold, dry polar regions but the cool, moist middle latitudes( not but rather is correct construction)
(C) glaciers are the cool, moist middle latitudes rather than the cold, dry polar regions( correct)
(D) glaciers, instead of being the cold, dry polar regions, would be the cool, moist middle latitudes( instead of being the cold dry polar regions modifies the glaciers,incorrect)
(E) glaciers are, instead of the cold, dry polar regions, rather the cool, moist middle latitudes(use of instead of and rather is not correct)
Will go with choice C
Thanks