Premise:In mammals it is the secondary palate that permits breathing while eating.
Conclusion: Clearly, breathing while eating is necessary to maintain the high rate of metabolism of mammals.

The author's assertions would be most weakened by the discovery of a mammalian species that had a
Prethink:Cause-effectTo weaken, hurt the co-relation of high metabolism to breathing
POE:
(A) high rate of metabolism and the ability to breathe while eating
(B) low rate of metabolism and the ability to breathe while eating ----> Similar to prethinking keep
(C) low rate of metabolism and no ability to breathe while eating
(D) high rate of metabolism and no secondary palate-----> Correct as This is hurting the most. No secondary palate, still high metabolism;REmoving the "cause" still effect exists
(E) low rate of metabolism and a secondary palate