The salinity of ocean water, commonly measured in parts per thousand (ppt), varies considerably depending on geographical location and climate...
GMAT Standard English Conventions : (Grammar) Questions
The salinity of ocean water, commonly measured in parts per thousand (ppt), varies considerably depending on geographical location and climate conditions. Compared with that of tropical ocean waters—where high temperatures accelerate evaporation and concentrate dissolved salts— ______
Which choice completes the text so that it conforms to the conventions of Standard English?
polar waters have a salinity level that is substantially lower.
when ocean waters are in polar regions, their salinity level is substantially lower.
the salinity level of polar waters is substantially lower.
ocean waters in polar regions have substantially lower salinity levels.
Sentence Structure
- The salinity of ocean water,
- commonly measured in parts per thousand (ppt),
- varies considerably
- depending on geographical location and climate conditions.
- Compared with that of tropical ocean waters
- where high temperatures accelerate evaporation
- and concentrate dissolved salts—
- [?] (about polar waters having substantially lower salinity)
Understanding the Meaning
Let's start with the first sentence:
The salinity of ocean water varies considerably depending on geographical location and climate conditions.
- This tells us that different parts of the ocean have different salt levels.
- Location and climate affect how salty the water is.
Now the second sentence begins with:
- 'Compared with that of tropical ocean waters'
This is where we need to pay close attention to the word 'that.'
- What does 'that' refer to?
- Looking back, 'that' = 'the salinity'
- So we're reading: 'Compared with the salinity of tropical ocean waters...'
The sentence gives us more detail about tropical waters:
- 'where high temperatures accelerate evaporation and concentrate dissolved salts'
- In hot tropical areas, water evaporates faster, leaving more concentrated salt behind.
Now here's where we need to fill in the blank. Let's look at our choices:
- A: "polar waters have a salinity level that is substantially lower"
- B: "when ocean waters are in polar regions, their salinity level is substantially lower"
- C: "the salinity level of polar waters is substantially lower"
- D: "ocean waters in polar regions have substantially lower salinity levels"
What do we notice about the structure here?
- We're making a comparison: "Compared with [THING A]... [THING B]"
- THING A = "the salinity of tropical ocean waters"
- THING B must match the same type of thing for the comparison to work properly
Let's check what each choice is comparing:
- Choice A: Compares "the salinity" with "polar waters" (the waters themselves)
- That's like saying "Compared with the height of basketball players, short people..."
- We're comparing salinity to waters - not the same type of thing!
- Choice B: Compares "the salinity" with a "when" clause
- This makes it a conditional statement rather than a direct comparison
- Awkward structure
- Choice C: Compares "the salinity of tropical waters" with "the salinity level of polar waters"
- Salinity compared to salinity - same type of thing! ✓
- This maintains parallel structure
- Choice D: Compares "the salinity" with "ocean waters in polar regions"
- Like Choice A, comparing salinity to waters - not parallel
So we need Choice C because it's the only one that compares salinity to salinity, maintaining the parallel structure required for proper comparisons.
The complete sentence means: Tropical waters have high salinity (due to evaporation), and when compared to that, polar waters have substantially lower salinity.
GRAMMAR CONCEPT APPLIED
Maintaining Parallel Structure in Comparisons
When you use comparison words like "compared with," "compared to," or "like," the elements being compared must be grammatically parallel - the same type of thing:
Pattern: "Compared with [THING A], [THING B]..."
THING A and THING B must be the same type
Example 1:
- Correct: "Compared with the speed of cheetahs, the speed of house cats is much slower."
- Speed compared to speed
- Incorrect: "Compared with the speed of cheetahs, house cats are much slower."
- Speed compared to cats (not parallel)
Example 2:
- Correct: "Compared with the size of Jupiter, the size of Earth is tiny."
- Size compared to size
- Incorrect: "Compared with the size of Jupiter, Earth is tiny."
- Size compared to planet (not parallel)
In this question:
- "that" = "the salinity" (pronoun referring back)
- Structure: "Compared with the salinity of tropical ocean waters, the salinity level of polar waters is substantially lower."
- Both sides of the comparison are about salinity → parallel ✓
- This is called maintaining parallel structure (or parallelism in grammar terms) - ensuring that compared elements match in grammatical form and logical category
polar waters have a salinity level that is substantially lower.
✗ Incorrect
- This compares "the salinity of tropical ocean waters" with "polar waters" (the waters themselves, not their salinity)
- Creates an illogical comparison between a characteristic (salinity) and the thing that possesses it (waters)
- Not grammatically parallel - you can't compare salinity to waters
when ocean waters are in polar regions, their salinity level is substantially lower.
✗ Incorrect
- This compares "the salinity of tropical ocean waters" with a conditional "when" clause
- Not parallel - comparing a noun phrase to a dependent clause
- Awkward structure that doesn't follow standard comparison conventions
the salinity level of polar waters is substantially lower.
✓ Correct
Correct as explained in the solution above.
ocean waters in polar regions have substantially lower salinity levels.
✗ Incorrect
- Like Choice A, this compares "the salinity of tropical ocean waters" with "ocean waters in polar regions"
- Not parallel - comparing a characteristic to the thing itself
- Creates the illogical structure: "Compared with [salinity]... [waters] have..."