We start, as always, by reading the initial sentence looking for one of the errors that we know GMAT test writers are wont to introduce into these sentences. We find none.

Then we look at the differences between the answer choices. We find that some choices say economic whereas others say economical.

What's the difference between economic and economical? Economical means affordable or inexpensive. For example, "We stayed at an economical hotel."

Economical is not the intended meaning of the sentence. Accordingly, we can eliminate choices B, D, and E.

Sentence (A) contains the correct idiom: so x that (arguably the most tested idiom on the GMAT). There is no reason to believe that (C) improves on it. Although the phrase so x as to y could be idiomatically correct, this sentence does not follow that format, rather it inserts the words "is it" into the idiom unnecessarily.