Hello Everyone!
This is a great example question you might find on the GMAT exam! Let's start by taking a quick look at the question, and highlight any major differences between the options in orange:
Laos has a land area about the same as Great Britain but only four million in population, where many are members of hill tribes ensconced in the virtually inaccessible mountain valleys of the north.
(A) about the same as Great Britain but only four million in population, where many
(B) of about the same size as Great Britain is, but in Laos there is a population of only four million, and many
(C) that is about the same size as Great Britain's land area, but in Laos with a population of only four million people, many of them
(D) comparable to the size of Great Britain, but only four million in population, and many
(E) comparable to that of Great Britain but a population of only four million people, many of whom
While it looks like there is a lot here that's different about each option, there are some things we can focus on to eliminate wrong options:
1. about the same / about the same size / comparable to the size / comparable to that
2. in population / a population
3. where many / and many / many of them / many of whom
Let's start with #1 on our list. If we look carefully, this has to do with parallelism! We need to make sure each sentence is comparing two items that are parallel in structure, type, number, wording, etc. Here is how each sentence handles the comparison between the land area of Laos and the land area of Great Britain:
(A) about the same as Great Britain but only four million in population, where many
land area of Laos + the entire country of Great Britain = NOT PARALLEL
(B) of about the same size as Great Britain is, but in Laos there is a population of only four million, and many
land area of Laos + the size of Great Britain = NOT PARALLEL
(C) that is about the same size as Great Britain's land area, but in Laos with a population of only four million people, many of them
land area of Laos + land area of Great Britain = PARALLEL
(D) comparable to the size of Great Britain, but only four million in population, and many
land area of Laos + the size of Great Britain = NOT PARALLEL
(E) comparable to that of Great Britain but a population of only four million people, many of whom
land area of Laos + land area of Great Britain = PARALLEL
We can eliminate options A, B, and D because they do not have parallel comparisons between the land areas of both countries!
Now that we have it narrowed down to only 2 options, let's take a closer look at each and determine which is the best option. To make errors easier to catch, let's add in the non-underlined parts of the sentence:
(C) Laos has a land area that is about the same size as Great Britain's land area, but in Laos with a population of only four million people, many of them are members of hill tribes ensconced in the virtually inaccessible mountain valleys of the north.
This is INCORRECT for a couple reasons. First, there is a missing comma between "Laos" and "with" because the phrase "with a population of only four million people" was turned into a non-essential clause that needs to be surrounded by commas. Second, if we treat the phrase "with a population of only four million people" as a non-essential phrase, the pronoun "them" doesn't have a clear antecedent. Who is "them" referring to? It's not clear - and the GMAT requires that all pronouns have absolutely clear antecedents!
(E) Laos has a land area comparable to that of Great Britain but a population of only four million people, many of whom are members of hill tribes ensconced in the virtually inaccessible mountain valleys of the north.
This is CORRECT! It compares the land are of Laos to the land area of Great Britain using parallelism, and the modifier that begins with "many of whom" is clearly referring back to "four million people," which makes sense!
There you have it - option E is the correct choice! If you know some of the tendencies of GMAT test writers, it's a lot easier to spot frequently used grammatical errors!
Don't study for the GMAT. Train for it.