Official Explanation
A question about the first peoples in the Americas.
Split #1: verb tense, beginning of underlining
The sentence begins with a past hypothetical possibility, and then, the verb at the beginning of the underlining has to be a verb that is similarly hypothetical but happened earlier than the action of the “if” clause.
Choice (A): “they would have had to have traversed” = hypothetical & earlier
Choice (B): “they would have to traverse”= hypothetical, but present/future = incorrect
Choice (C): “they had to traverse” = factual and simple past = incorrect
Choice (D): “they had to have traversed” = factual past perfect = incorrect
Choice (E): “they would have had to have had traversed” = iffy: the past perfect infinitive is extremely rare and unneeded after the main verb = incorrect.
Split #2: verb tense, end of underlining
Here, the difference is whether the obligation to account for something is itself in the present or the past. Context does not make clear which, so either is fine. All five choices are correct here.
Split #3: verb tense, part three
Choice (E) has an odd tense pairing: the journey “would have been” (hypothetical past) impossible, and thus first people “had come” (past perfect) much later (??). If that later action is “much later,” why is it in the past perfect, which emphasizes that it was earlier. This is a tense mismatch. Choice (E) is incorrect.
Split #4: pronoun
The beginning of the underlining talking about the people journeying across all the ice, an action given by a verb. We cannot use a pronoun to refer to the action of a verb. We have to refer to this by saying something such as “such a journey,” as in (A) & (E). Choices (C) & (D) use the pronoun “this” to refer to the action of the previous clause: a clear pronoun mistake. Choices (C) & (D) are incorrect.
Split #5: logic
In choice (B), the phrasing “those who argue against this impossible journey” is quite odd. It’s one thing to argue that the journey was impossible—such seems the opinion of some scholars. But the phrasing here seems to assume that we already know that the journey is impossible, and the opinion expressed is that one shouldn’t try this thing known to be impossible—really great advice here: don’t do anything impossible! Furthermore, the sentence here shouldn’t simply assume that the journey is impossible, since the first part of the sentence discusses the possibility of this journey. There are layers of logical problems here. Choice (B) is incorrect.
The only possible choice is (A).