Thanks for the question! So we’re asked to figure out what methods of reasoning the author’s NOT using in the argument (since this is an EXCEPT question). First, let’s recap the argument: we’re asked if people who pluck out their gray hairs don’t like the elderly as much as those who don’t. Then, we’re told there’s no necessary condition, since you might like the elderly but not like impaired eyesight and hearing. And not liking older people because they’re old is immoral, but it’s ok to not like some parts of the aging process.
OK, so now let’s take a look at (A). Does the author dismiss an assertion as unfounded? Well, yes, when the author says “there is no necessary connection.” When she says that, she’s dismissing the assertion that people who pick out their gray hairs do have more negative attitudes toward the elderly. So (A) is something that the author does, and must be eliminated.
Now let’s take a look at (D). Does the author discredit a common stereotype about the elderly? Well, no, that doesn’t happen anywhere in the passage! That would look something like “well, people think elderly people are slow, but actually they’re not,” but nothing like this ever happens. So (D) doesn’t happen, and is the correct answer choice.
Hope this helps! Feel free to ask any other questions that you might have.