While researching a topic, a student has taken the following notes:Planetary scientists classify asteroids based on their composition.C-type asteroids...
GMAT Expression of Ideas : (Expression) Questions
While researching a topic, a student has taken the following notes:
- Planetary scientists classify asteroids based on their composition.
- C-type asteroids are composed primarily of carbon.
- They account for roughly 75 percent of known asteroids.
- S-type asteroids are primarily made up of silicate minerals.
- They account for roughly 17 percent of known asteroids.
The student wants to emphasize a difference between C-type and S-type asteroids. Which choice most effectively uses relevant information from the notes to accomplish this goal?
Planetary scientists classify asteroids into types, two of which are the C-type and the S-type.
Planetary scientists consider an asteroid's composition (such as whether the asteroid is composed mainly of silicate minerals or carbon) when classifying it.
Roughly 17 percent of known asteroids are classified as S-type asteroids; another percentage is classified as C-type asteroids.
C-type asteroids are mainly composed of carbon, whereas S-type asteroids are primarily made up of silicate minerals.
Step 1: Decode and Map the Passage
Create Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| 'Planetary scientists classify asteroids based on their composition.' |
|
| 'C-type asteroids are composed primarily of carbon.' |
|
| 'They account for roughly 75 percent of known asteroids.' |
|
| 'S-type asteroids are primarily made up of silicate minerals.' |
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| 'They account for roughly 17 percent of known asteroids.' |
|
Provide Passage Architecture & Core Elements
Main Point: Planetary scientists classify asteroids into different types based on composition, with C-type and S-type being the two most common categories.
Argument Flow: The notes first establish that scientists classify asteroids by composition, then systematically present two major types (C-type and S-type), giving both their compositional makeup and their relative frequency among known asteroids.
Step 2: Interpret the Question Precisely
What's being asked? We need to find which choice most effectively emphasizes a difference between C-type and S-type asteroids.
What type of answer do we need? A sentence that highlights a contrast or distinction between these two asteroid types using information from the notes.
Any limiting keywords? 'Emphasize a difference' is key - we need something that actively contrasts the two types, not just mentions them separately.
Step 3: Prethink the Answer
- From our notes, we have two clear differences between C-type and S-type asteroids:
- Composition difference: C-type are made of carbon vs. S-type made of silicate minerals
- Frequency difference: C-type make up 75% vs. S-type make up 17%
- To 'emphasize a difference,' the correct choice should directly contrast these asteroid types, probably using language that sets up a comparison (like 'while,' 'whereas,' 'unlike,' etc.)
- The most fundamental difference is their composition since that's what the classification system is based on
- The right answer should directly contrast the composition of C-type and S-type asteroids in a way that makes their difference clear and prominent
Planetary scientists classify asteroids into types, two of which are the C-type and the S-type.
- Simply states that both are types of asteroids classified by scientists
- Doesn't emphasize any difference between them - just groups them together
- Misses the opportunity to highlight what makes them distinct
Planetary scientists consider an asteroid's composition (such as whether the asteroid is composed mainly of silicate minerals or carbon) when classifying it.
- Mentions composition as a classification factor and gives examples of both materials
- Doesn't directly connect carbon to C-type or silicate minerals to S-type
- Students might think this works because it mentions both materials, but it doesn't create a clear contrast between the asteroid types themselves
Roughly 17 percent of known asteroids are classified as S-type asteroids; another percentage is classified as C-type asteroids.
- Mentions the 17% figure for S-type but vaguely refers to C-type as 'another percentage'
- Doesn't specify that C-type asteroids make up 75%
- Completely ignores the composition difference, which is more fundamental
C-type asteroids are mainly composed of carbon, whereas S-type asteroids are primarily made up of silicate minerals.
- Uses 'whereas' to create a direct contrast between the two asteroid types
- Clearly states both compositional differences: carbon vs. silicate minerals
- Matches our prethinking by emphasizing the fundamental difference that drives the classification system
- Most effectively uses the relevant information to accomplish the goal of emphasizing difference