samgyupsalI can see why E might feel okay, since the relative pronoun "those" (like the singular "that") has some flexibility. We often use "those" to refer back to a base noun while changing its modifiers. For instance, in the sentence, "Rich people sometimes pay less income tax than those with lower incomes," "those" refers to "people" and not "rich people."
However, the flexibility of "those" can create problems when it's not clear which modifiers are meant to be left behind. If I say "both contemporary Hispanic authors living abroad and those in the United States," what does "those" refer to? Contemporary Hispanic authors? Hispanic authors? Contemporary authors? Also, the fact that we have two different forms of modifier ("living abroad" and "in the United States") makes things worse. B fixes the problem by using "those" to refer to the entire noun phrase: "contemporary Hispanic authors" and then applying similar modifiers to each to make the contrast clear.
A simpler way to think about this whole issue might be to consider that when we use the "both . . . and" construction to refer to two different cases, we want to describe the difference as clearly and directly as possible. For that reason, when I see "both contemporary Hispanic authors and," I expect it to be followed by something like "18th century Greek authors." In other words, if we aren't planning to contrast the "contemporary Hispanic" part, why are we putting it into the "both . . . and" construction? It's much easier to say "contemporary Hispanic authors both abroad and in the US," since the "contemporary Hispanic author" part is common to both groups.
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