IMO, this question is terrible. In fact, the current version on GMAT Pill's website (
https://www.gmatpill.com/gmat-practice-t ... stion/1221) adds other issues to E so that C becomes the best answer. An official comment even says that it would be okay to use the form of E.
Even with the change, however, I think C still fails. Here's why:
We use "those" in a comparison to refer to something apart from our discussion. For example, "these are mine, but those are yours." Another example, "These humans are taller than those humans."
In C, we have a comparison and "those" is referring to "humans", but that would only make sense if we are referring to two distinct groups. So you might say that we are, right? Humans now and humans at other times? Well the problem with this is that we never identify the first group to be distinct from "those" humans at other times.
When we talk about a species, we refer to the entire group at once, unless we quantify it. For example, "humans have been around for 200,000 years" refers to all humans at all times.
Applying this to the question, we see that the sentence with answer C again refers to all humans at all times because it never qualifies or quantifies humans - it just says that "technology has allowed humans" to do something. This creates a problem when we compare humans in general (it's not specific in C because C doesn't keep "now") to those at other times.
That's almost like telling 10 students that they as a group are smarter than a subset of 3 of them -while that could mathematically work, the intended meaning is more likely to be comparing a subset to a subset, as it is for this question. That's not exactly the same but I hope it's close enough to demonstrate why it's wrong to compare a whole group to a subset of that group in this case.
So we could properly write the sentence in at least these two different ways:
* The modern rise of mobile, social, and location-based technologies has allowed today's humans to be more tech-savvy than those at any other time in history.
If we want to keep "those", we can't continue to refer to humans as a group and then compare all of them to a subset. This formulation fixes it by restricting the initial humans to "today's humans" only.
We might also say "humans now" or something else, but that might not identify the correct group as well as this for a few reasons.
* The modern rise of mobile, social, and location-based technologies has allowed humans to become more tech-savvy now than at any other time in history.
This works because, while it's still taking about humans in general, it keeps that throughout. You can read it as "has allowed humans to become more tech-savvy now than (they have been) at any other time in history." This is good because we are referring to all humans as the human species and we compare a characteristic of the group "now" to a characteristic of the group at "any other time". We do this a lot when referring to species. For example "giraffes are taller now than ever before" or "giraffes are taller now than they ever have been".
This is almost E in this version of the question (again, GMAT Pill has a different E to make it more wrong), but E losses the proper time comparison by omitting "other" (so it compares a characteristic of humans now to a characteristic of humans at all times).
The moral of the story? Don't use non-official GMAT sentence correction questions because many of them are fatally flawed. For this one, all answers fail. Just because some "expert" gives you an explanation, that doesn't mean it is correct.
Also, as a side note, ambiguity should be the last thing that you consider. Many questions have ambiguous pronouns in the correct answers. That's okay because ambiguity is like being concise. Failing to do so doesn't make it incorrect, it just makes it less preferable if other answers are also grammatically ok and also have the correct meaning.