Hey Sana,

Hemant's response here is pretty great. I can add a couple other things.

Acid rain is considered not yet so serious a problem in the West as in the East, where hundreds of lakes have been rendered sterile by increased acidity.
(b) considered not so serious a problem yet in the West as
(c) not yet considered so serious a problem in the West as it is
(d) not considered as yet the serious problem in the West that it is
(e) not as yet considered that serious a problem in the West as

(A) "not yet" error. Missing "it is" for the comparison.
(B) the "not" needs to go before considered, rather than after it. Missing "it is" as well.
(C) correct.
(D) The "the" before "serious problem" makes it sound like there's a specific problem in the West. "not yet error".
(E) "that" doesn't set up the comparison (we need "so" or "as")

Hope that helps!

-t

Hey Rajat,

It's hard to separate out what is an idiom or comparison error here, as they get mashed together. (B)'s comparison is pretty bad, because it seems to be comparing "Acid rain" to "in the East". As if "in the East" is another kind of problem. See what I mean? Sana's point is also good. (B) is just all around icky.

-t