PT14.S2.Q07 - all zebras have stripes

ChiTownGuy

Can someone help me with this question? I don't know why A is wrong and D is right, they said that you should strengthen the argument that stripes serve as signal for other zebras. Honestly this one kind of pissed me off.

nye8870

ac-A says "The subspecies of zebras with the best-defined stripes is also characterized by exceptional size and vigor." To me. this does not strengthen the conclusion because it does not address the communicative properties of stripes.
ac-D says "Zebras react much faster to moving shapes that have stripes than they do to moving shapes that are otherwise identical but lack stripes." To me, this further explains the way stripes contribute to zebra reactivity by adding a comparison with their non-reactiveness to plain colored objects.