Why not C?

When we are evaluating arguments, keep in mind that we usually need to examine the argument itself, and not the person making it. There are times when the flaw could be "the conclusion relies on the testimony of someone who is not an expert," but this is not one of those times. The author proceeds basically by calling Weingarten a hypocrite, and therefore his argument should be rejected. This is reflected by answer choice E, but why is E correct? Maybe Weingarten is wrong about pets, and owning a pet is truly unethical. It doesn't matter in this case, because it doesn't really affect the zoo argument. The author has introduced the pet example in the hopes of questioning Weingarten's credibility. However, the author has said nothing to weaken the claim that keeping animals in a zoo is unethical. The only reasoning the author gives, is that Weingarten is wrong about one thing, so he must be wrong about the other thing. This is not enough to reject his conclusion, which is why the argument is flawed.

Thank you, this was very helpful!