The stem says nothing about redundancy, or at least nothing that would let us draw an inference about it. So A, B and C aren't correct. And the stem tells us nothing about what would be true if the "human auditory system is a perfect receptor", so D can't be correct. The stem only tells us what is true if the auditory system is imperfect, so that's the only situation we can draw an inference about. So you could reach E by elimination.
E is correct, but the wording is so complicated (much more LSAT-like than GMAT-like) that it makes sense to simplify it a lot to see the logical connections. Paraphrasing the last sentence of the stem, "if ears are imperfect, then some sound combinations are not understandable words". The second last sentence says, similarly simplifying, "if a language is efficient, every sound combination is an understandable word". So it cannot simultaneously be true that ears are imperfect and a languages is efficient, since those two premises lead to contradictory conclusions, and that's why E is a correct inference.
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