Explanation

Creating a filter: no error jumps out in the sentence. "So that" is a valid idiom. We'll try to eliminate the other answer choices by finding objective defects.

Choice (B) introduces wordiness with no gain, and without a "that" in place of a comma, it creates a run-on sentence. In (C), "it is such that" is not a valid phrase and uses a pronoun that has no reference. Choice (D) has the same problems as (B). "Severity and intractability" would appear to describe the kind of severity, not the degree. (E) is not a run-on, but it describes severity and intractability as if they are easily quantifiable (with "so much") and generally present around us (with "there is"). The correct answer is (A).