1. The form in option A, so gradual as to be indistinguishable is correct.

2. In option B, so gradual so that should be so gradual that.

3. In option C, so gradual that is fine, but that they are unable to be distinguished makes little sense. In they are unable, there is a doer: the SHIFTS. In to be distinguished, there is no stated doer: the construction is passive. The combination of the two creates an unclear notion. (One would say, for example that He was unable to make himself understood and not He was unable to be understood. The doer has got to be the one who performs the action expressed first in the finite verb and then in the infinitive.) Furthermore, in the GMAT the adjectives ABLE and UNABLE are applied to living organisms, not to phenomena such as ECONOMIC SHIFTS.

4. In option D, not to be indistinguishable means that the shifts are distinguishable, and this is the opposite of the intended meaning of the sentence, as that meaning is expressed in option A.

5. In option E, gradual enough so that is ungrammatical. Moreover, SO THAT introduces objectives, not consequences, as it attempts to do here.

Therefore, the form in option A, SO + ADJECTIVE + AS + INFINITIVE is a correct (though less-frequently used) alternative to SO + ADJECTIVE + THAT.


If you like this post, please click on the THANK button.

You can also visit us at https://www.xgmat.com/
[/i]

Great explanation fabio.
this Sc now makes a lot of sense to me.
Thanks alot