diagramming type, etc..

@chris_va, We can diagram the question the following way: (1) If a spoken language is completely efficient, then every permutation of its basic language can be an understandable word. E-> UW IF efficient THEN an understandable word (2) If the human auditory system is an imperfect receptor of sounds, then it is not true that every possible permutation of a spoken language's basic sounds can be an understandable word. ~PR -> ~UW IF NOT a perfect receptor THEN NOT an understandable word Which of the following must be true? ~PR > ~UW is logically equivalent to: UW -> PR that can be combined with premise (1) to form: E->PR that is logically equivalent to: ~PR -> ~E If NOT a perfect receptor then NOT efficient That is the same statement as in the correct answer choice (E). Let me know if you have any further questions.