Breaking down a Long GMATPrep SC problem

by , Mar 8, 2011

A student recently asked me what they should do when faced with Sentence Correction problems containing very long underlines and a jumble in the answer choices. Many sentence correction questions can easily be scanned vertically, in order to find differences among the answers. But in some problems, major parts of the sentence move around and the basic structure changes (for instance, an independent clause becomes dependent and vice versa). If youre a ManhattanGMAT student, we would classify these kinds of questions as ones for which the splits are more challenging to identify.

This week and next were going to analyze a couple of GMATPrep^ Sentence Correction questions that possess these characteristics. (Note: click here to read about the general process of attacking Sentence Correction questions; the techniques we discuss in this current article are to be used only when necessary.)

Heres today's problem; set your timer for 1 minute and 15 seconds and go!

More than 300 rivers drain into Siberias Lake Baikal, which holds 20 percent of the worlds fresh water, more than all the North American Great Lakes combined.

(A) More than 300 rivers drain into Siberias Lake Baikal, which holds 20 percent of the worlds fresh water, more than all the North American Great Lakes combined.

(B) With 20 percent of the worlds fresh water, that is more than all the North American Great Lakes combined, Siberias Lake Baikal has more than 300 rivers that drain into it.

(C) Siberias Lake Baikal, with more than 300 rivers draining into it, it holds more of the worlds fresh water than all that of the North American Great Lakes combined, 20 percent.

(D) While more than 300 rivers drain into it, Siberias Lake Baikal holds 20 percent of the worlds fresh water, which is more than all the North American Great Lakes combined.

(E) More than all the North American Great Lakes combined, Siberias Lake Baikal, with more than 300 rivers draining into it, holds 20 percent of the worlds fresh water.

[Note to those who answered the problem within the allotted time frame and thought it wasnt too hard. Did you read the answer choices horizontally? Or did you compare choices vertically? You may be able to get away with a horizontal strategy for this problem, but if you want to get better, then you need to learn the vertical strategy for harder problems. If this problem was easier for you, dont dismiss it. Use it to learn how to tackle harder problems. (And use this principle in general: easier problems are VERY good for learning how to tackle harder problems.)]

Okay, have you got your answer? Now, lets dive into this thing!

What did you think when you read the original sentence?

The first thing I noticed was that the entire sentence is underlined. Thats a really good clue that I might have one of these sentences where the splits (or differences in the answer choices) might be less obvious. Its more likely that big chunks of the sentence will move around, and the forms of different pieces may change more substantially than usual. Basically, the longer the underline, the more likely it is that you will see these types of things in the answer choices.

More than 300 rivers drain into Siberias Lake Baikal*, WHICH **holds an amount of water, MORE THAN*** <the water in another area>.

* The opening piece is our independent clause (main sentence): More than 300 rivers drain into Siberias Lake Baikal. (Note that more than here is not introducing a comparison. It is simply defining a number: more than 300.)

** The which introduces our first modifier. Which indicates a noun modifier, and a comma which structure should modify the closest preceding main noun. In this case, the closest preceding main noun is Lake Baikal.

*** The second instance of more than indicates a comparison. We need to make sure that the items being compared are both logically and structurally comparable. In this case, were comparing the amount of water contained in one lake to the amount of water contained in several other lakes combined. [Note: because more than appears after the comma, it is carrying the concept under comparison (a percentage of the worlds fresh water) to the second comparison item; that is, we are comparing the relevant worlds fresh water percentage figure for Lake Baikal and the Great Lakes.]

More simply, weve got:

Independent clause, modifier, comparison

In general on SC, if you spot something that you think is problematic when reading the initial sentence, then you address that issue first. If you dont spot something, or you dont see anything more in the original (but you still have more than one answer choice remaining), you need to do one of two things:

(1) start reading the remaining answers horizontally, or

(2) start comparing the remaining answers vertically.

As a general rule, it is preferable to compare answers vertically. Your goal is always to find the best answer of the five; finding the best of something is by definition a comparison.

On many SC problems, this vertical comparison is relatively straightforward: you notice that three answers have the verb is and two have the verb are, so now you know there is a subject-verb issue and you need to identify the subject in order to know whether is or are is the right verb. On some SC problems, however, the vertical comparisons are not that easy but that doesnt mean you cant still use the technique!

So how do we still use this technique when the splits, or differences, arent as straightforward? We break the sentence into major parts thats why I simplified our original sentence, above, into independent clause, modifier, comparison.

Where are those parts in the various answer choices? Answer choice A is always the same as the original, of course. What about the others?

Answers B, C, D, and E all open with some kind of modifier, not an independent clause. So the independent clause moves, but we know the sentence still needs to contain an independent clause somewhere! So what are the structures of the five sentences? (The commas represent the actual commas found in the sentences.)

A: independent clause, modifier, comparison

B: modifier, comparison, independent clause

C: subject (beginning of independent clause), modifier, independent clause (containing comparison), modifier

D: comparison, independent clause, modifier (containing another comparison)

E: comparison, subject (beginning of independent clause), modifier, rest of independent clause

In practice, I would start just with the independent clause in each choice, ignoring the rest of the sentence. Is each independent clause okay?

So, lets see. We do have independent clauses in each option, so we cant eliminate for that reason (sometimes, an answer wont contain an independent clause at all). There is something funny about the independent clause in C, though what is it?

C: Siberias Lake Baikal it holds more of the worlds fresh water than all that of the North American Great Lakes combined

Ah. The independent clause has two subjects: Lake Baikal and the pronoun it. Sentences can have two subjects, but those two subjects need to have a connector word, such as and or or, in between. Choice C says Lake Baikal it holds. No good. Eliminate C.

What else? The independent clause is jumping around, and so are the modifiers that hang on the clause. Looks like we need to check whether the big pieces are placed correctly relative to the other big pieces!

Hmm. Noun modifiers are supposed to be placed as close as possible to the nouns they modify in the vast majority of cases, right next to the nouns they modify. Let's grab each modifier and check its placement (ignoring everything else in each sentence).

A: Lake Baikal, which holds 20 percent of the worlds fresh water Does Lake Baikal hold that water? Yes. A is okay on this count.

B: With 20 percent of the worlds fresh water, that is more than all the North American Great Lakes combined What is with 20 percent of the water? That? North American Great Lakes? No. Its supposed to be Lake Baikal, but that doesnt even show up until after the comparison. No good. Eliminate B.

C: Already eliminated, but note that the 20 percent is placed incorrectly. Does Lake Baikal contain 20 percent of the water, or does that 20 percent refer to the North American Great Lakes combined? I have no idea. This would be another reason to eliminate C.

D: While more than 300 rivers drain into it, Siberias Lake Baikal Is the modifier info referring to Lake Baikal? Yes. Thats okay as far as that goes. But there is a sticking point. What does the word while mean? It can actually mean two things:

  1. while = at the same time as. I practice piano while twiddling my thumbs. (Im very talented!) I practice piano at the same time as I twiddle my thumbs.
  2. while = although, or some sort of contrast. While its true that I play piano and know how to twiddle my thumbs, I obviously cant do both of those things at the same time. That would be impossible!

In this case, neither of those interpretations would make sense for this sentence. It doesnt make sense to say that the 300 rivers drain into Lake Baikal at the same time as the lake holds 20 percent of the worlds fresh water. These arent two separate actions that happen to occur simultaneously.

Nor does it make sense to introduce a contrast: although the 300 rivers drain into Lake Baikal, the lake holds 20 percent of the worlds fresh water. Actually, the Lake holds that much fresh water because the 300 rivers drain into it, not despite this fact.

So, although the placement of the modifier in D is okay, the introduction of the word while to introduce the modifier is not. Eliminate D.

E: Lake Baikal, with more than 300 rivers draining into it Is the modifier referring to the preceding noun, Lake Baikal? Yes. Some people may object that the modifier sounds awkward, in particular the pronoun it. I agree that it sounds awkward, but were going to stick to solid grammar rules here. The modifier refers to the correct noun.

Weve eliminated B, C, and D; we still have A and E. What havent we tested yet? The placement of the comparison lets try that next.

A: Lake Baikal, which holds 20% of the worlds fresh water, more than all the North American Great Lakes combined. The second half of the comparison is clear: the North American Great Lakes combined. The first half refers to the thing that holds 20% of the worlds fresh water: Lake Baikal. Lake Baikal holds 20% of the water and that figure is more than the equivalent figure for the collective Great Lakes.

E: More than all the North American Great Lakes combined, Siberias Lake Baikal So Lake Baikal is more than the Great Lakes more than what? What specific measurement are we discussing? General size or volume? The number of rivers draining into each? The percentage of the worlds fresh water that each holds? Ambiguity = bad. Eliminate E.

The correct answer is A.

Key Takeaways for Long Underlines + Jumbled Sentences on SC

(1) Long-underline sentences are more likely to be jumbled that is, to move big chunks of the sentence around and even to change what information is located in the dependent vs. independent clauses. When you see this happening, you need to break the sentence down into those chunks (commas are often great natural separators) and figure out the role of each chunk.

(2) When you use the chunk strategy, you will often start in one of two places: either start with the first chunk of the original sentence and go find the location of that chunk in subsequent answer choices, or start with the independent clause in each answer choice, wherever that might be.

(3) These kinds of sentences also typically test the placement of the chunks is the modifier or comparison in the right place relative to the other pieces of information? Is the parallelism constructed properly across the sentence?

Finally, join us next week for more on this topic as we tackle another, even more convoluted problem of this type!

^GMATPrep question courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.

Read Part 2 of this article by clicking here.