While researching a topic, a student has taken the following notes:Earthquakes start at a point called a 'focus' and spread...
GMAT Expression of Ideas : (Expression) Questions
While researching a topic, a student has taken the following notes:
- Earthquakes start at a point called a 'focus' and spread out from there as seismic waves.
- The two types of seismic waves that travel beneath Earth's surface are primary waves (P waves) and secondary waves (S waves).
- P waves travel more quickly beneath Earth's surface than do S waves.
- P waves compress and expand the ground, causing it to move backward and forward.
- S waves cause the ground to move from side to side.
The student wants to emphasize a similarity between P waves and S waves. Which choice most effectively uses relevant information from the notes to accomplish this goal?
P waves and S waves both travel beneath Earth's surface, causing the ground to move.
P waves travel away from an earthquake's starting point at a higher rate of speed than do S waves.
Spreading out from the focus of an earthquake, P waves move the ground backward and forward.
Although P waves and S waves start at the same point, they behave very differently.
Step 1: Decode and Map the Passage
Part A: Create Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| 'Earthquakes start at a point called a 'focus' and spread out from there as seismic waves.' |
|
| 'The two types of seismic waves that travel beneath Earth's surface are primary waves (P waves) and secondary waves (S waves).' |
|
| 'P waves travel more quickly beneath Earth's surface than do S waves.' |
|
| 'P waves compress and expand the ground, causing it to move backward and forward.' |
|
| 'S waves cause the ground to move from side to side.' |
|
Part B: Provide Passage Architecture & Core Elements
Main Point: There are two types of seismic waves (P and S waves) that both travel beneath Earth's surface but work differently in terms of speed and how they move the ground.
Step 2: Interpret the Question Precisely
This is a fill-in-the-blank question asking us to choose the best logical connector. The answer must create the right relationship between what comes before and after the blank.
Step 3: Prethink the Answer
- From our analysis, P waves and S waves share several key similarities:
- Both are seismic waves that travel beneath Earth's surface
- Both cause the ground to move (even though the movement patterns differ)
- Both spread out from the earthquake's focus
- The correct choice should highlight one or more of these commonalities while avoiding emphasizing their differences like speed or movement patterns
P waves and S waves both travel beneath Earth's surface, causing the ground to move.
- States that both waves 'travel beneath Earth's surface' and both cause 'the ground to move'
- Directly emphasizes two major similarities from our notes
P waves travel away from an earthquake's starting point at a higher rate of speed than do S waves.
- Focuses on P waves traveling 'at a higher rate of speed than do S waves'
- Emphasizes a difference (speed) rather than a similarity
Spreading out from the focus of an earthquake, P waves move the ground backward and forward.
- Only discusses P waves and their movement pattern
- Provides no comparison or mention of S waves at all
Although P waves and S waves start at the same point, they behave very differently.
- Explicitly states that P waves and S waves 'behave very differently'
- Directly emphasizes differences rather than similarities