It is now a common complaint that the electronic media have corroded the intellectual skills required and fostered by the literary media. But several centuries ago the complaint was that certain intellectual skills, such as the powerful memory and extemporaneous eloquence that were intrinsic to oral culture, were being destroyed by the spread of literacy. So, what awaits us is probably a mere alteration of the human mind rather than its devolution.
The reference to the complaint of several centuries ago that powerful memory and extemporaneous eloquence were being destroyed plays which one of the following roles in the argument?
evidence supporting the claim that the intellectual skills fostered by the literary media are being destroyed by the electronic media
The author isn't trying to prove that electronic media are destroying literary skills. That's the complaint the author is responding to, not something the author believes.
an illustration of the general hypothesis being advanced that intellectual abilities are inseparable from the means by which people communicate
The author never advances a hypothesis that intellectual abilities are "inseparable from" the means by which people communicate. The author's point is about what happens when communication methods change: the human mind shifts rather than declines. That's a claim about the consequences of changing communication methods, not a claim that intellectual abilities and communication methods can't be separated.
an example of a cultural change that did not necessarily have a detrimental effect on the human mind overall
This captures the role precisely. The spread of literacy destroyed certain oral skills like powerful memory and extemporaneous eloquence. But the author treats this as a case where the human mind changed rather than got worse overall. The historical example is meant to show that losing one set of skills when a cultural change takes place (shift from oral to literate culture) doesn't necessarily mean the mind is declining."
evidence that the claim that the intellectual skills required and fostered by the literary media are being lost is unwarranted
This is tempting because the author does seem to push back against the current complaint about electronic media. But (D) goes further than the author does. (D) says the historical example is evidence that the current complaint is unwarranted, meaning the complaint is baseless or unjustified. That would mean the author is arguing that literary skills aren't actually being lost. But that's not her point. She's arguing that even if literary skills are being lost, that's OK, because it's just
possible evidence, mentioned and then dismissed, that might be cited by supporters of the hypothesis being criticized
The author doesn't mention and then dismiss the historical complaint. She relies on it as evidence supporting her conclusion. And the historical complaint isn't something "supporters of the hypothesis being criticized" would cite. The people complaining about electronic media today wouldn't point to the historical complaint about literacy to help their case, since that historical complaint undermines the idea that losing skills to a new medium is a disaster.