The conclusion of this argument is: the authors saying that no evidence exists to support the idea that the rate of extinction of animal species is now accelerating are wrong.
Why? The arguer presents data on fishes: "40 species and subspecies of North American fishes have vanished in the twentieth century, 13 between 1900 and 1950, and 27 since 1950."
So our conclusion is that a theory that no evidence exists to support the idea of a MASS extinction is wrong because we have data on the extinction of fishes. See how our evidence might not fully cover the entire scope of a mass extinction?
We must determine whether this fish species was representative of the other animals. If so, then the authors are, in fact, wrong because there is evidence. If the fishes are not representative of other animals, then this evidence does not support a mass extinction and merely gives us information on one specific type of animal.
Thus, we would need answer choice (A)--"were the fish species and subspecies that became extinct unrepresentative of animal species in general with regard to their pattern of extinction?"--to help us evaluate the argument.
Hope that helps! Please let us know if you have any more questions.
