Climatic shifts are so gradual as to be indistinguishable at first from orginary fluctuations in the weather.
(b) so gradual they can be indistinguishable
(c) so gradual that they are unable to be distinguished
(d) gradual enough not to be distinguishable
(e) gradual enough so taht one cannot distinguish them
Wouldn't the correct idiom be "so...that..."?
its clearly between A and C. I choose C over A first for "so........that" reason.
But I later realized that "Climatic shifts are unable to be distinguished" doesnot make sense to me. "they can be indistinguishable" makes more sense.
So A is my choice though it has "so as to", which is less common than "so .......that".