I had a request to answer this one. This question is from GMATPrep.
Often major economic shifts are so gradual as to be indistinguishable at first from ordinary fluctuations in the financial markets
A) so gradual as to be indistinguishable
B) so gradual so that they can be indistinguishable
C) so gradual that they are unable to be distinguished
D) gradual enough not to be indistinguishable
E) gradual enough so that one cannot distinguish them
The issues here are IDIOMS, MEANING, and CONCISION.
A) so gradual as to be indistinguishable
"so... as to be..." is a correct idiom.
B) so gradual so that they can be indistinguishable
"so... so that..." is not a correct idiom
C) so gradual that they are unable to be distinguished
This one is tough, because it's not grammatically or idiomatically incorrect. "So... that" is a correct idiom. It's certainly wordier than A, and there also seems to be a disconnect in meaning. If something is "indistinguishable," then
people are not able to distinguish it. Here, saying that the "shifts... are unable to be distinguished," then the lack of ability is on the part of the shifts, and not on the people distinguishing. This is a case in which passive voice alters the meaning slightly, and therefore makes less sense.
D) gradual enough not to be indistinguishable
"gradual enough" means something different from "so gradual." "Enough" implies a
sufficient quantity, above a certain threshold - "I have
enough money to by the new laptop." "So" is a qualifier meaning "to such a degree that." For example, "I have
so much money that I could buy all of the laptops in the world." It doesn't imply any threshold.
E) gradual enough so that one cannot distinguish them
Same issue as in D.
The correct answer is
A.