Patagonia, extending from the Rio Colorado in southern Argentina down

Magoosh Official Explanation:

First of all, we have some big grammar issues in the prompt. We have a noun "Patagonia", then a long modifier, then "and" and an independent clause. The word "and" can join two independent clauses, but it can't joint an independent clause to a fragment. This current structure is

[noun] + [modifier] + "and" + [independent clause]

This structure is completely wrong. For example, consider the following failure of a sentence: "George Washington, very honest, and Thomas Jefferson was a brilliant writer." That is a fundamentally ungrammatical sentence, and it is follows precisely the same grammatical structure as the prompt in this question. Reject (A).

Choices (C) & (D) have two independent clauses correctly joined by "and", so in that respect, they are acceptable. We'll come back to this pair.

Choice (E) changes the meaning. In (A)-(D), it's the entirety of Patagonia that "boasts numerous dramatic views …", but (E)'s phrasing makes it seem that only the Tierra de Fuego archipelago boasts these views. That changes the meaning too much, so this cannot be correct. (E) is wrong.

Both (C) & (D) have two independent clauses joined by "and", their modes of expression are profoundly different. (C) has wordy, awkward indirect language ---- it has "has an extent from" instead of "extends from." The GMAT SC doesn't like versions of a sentence that change a verb, such as "extends", to its noun form, "extent." Action should be in verb-form. Re-expressing action as a noun is generally wordier, more awkward, and more indirect. Another problem with (C): the way it ends doesn't flow smoothly into the rest of the sentence: "….views are numerous alpine lakes to …" For all these reasons, we have to reject (C).

This leaves (B) & (D). Let's consider what's wrong with (B). First of all, there is nothing grammatically wrong with (B). As a sentence by itself, it has no grammar flaws. The structure at the beginning is called an absolute phrase.

There are two reasons why (D) is a wholly better answer than (B).

1) Rhetorically, it's good to make a sentence have a strong focus. In this sentence, the focus, the start of the sentence should be "Patagonia". In (D), that's the very first word and the subject of both verbs --- the grammatical centrality reflects the rhetorical centrality. Choice (B) awkwardly keeps the subject, the focus, a secret for more than half the sentence. Imagine if (B) were spoken --- by the time you get to the word "Patagonia", many people would have forgotten the properties said about it at the beginning! ------ This issue, by itself, would not be the make-or-break deciding issue on a GMAT SC question.

2) The verb tense. Choice (B) changes the verb tense from the present. Everything in the prompt and in (D) is in the present tense, pure and simple. Choice (B) changes to the present perfect, a subtle change in meaning. This is highly suspect, and combined with problem #1, this is enough to reject (B).

Choice (D) has two direct active clauses, expressing the information elegantly and powerfully, with no grammatical errors. (D) is correct.