Question 81·Hard·Transitions
Efforts to map the ocean floor once relied on echo sounding, which sends sound pulses to the seabed and records the returning echoes. The technique produces accurate depth readings directly beneath a vessel but leaves vast spaces between survey lines unresolved. ______ satellite altimetry measures slight variations in sea-surface height that correspond to features on the ocean floor, enabling researchers to infer bathymetry over wide areas.
Which choice completes the text with the most logical transition?
For transition questions, always read at least one sentence before and after the blank and summarize their relationship in your own words (for example: contrast, cause/effect, example, or addition). Once you’ve named the relationship, quickly label each answer choice by the type of connection it signals and eliminate any whose meaning doesn’t match your summary; avoid being distracted by how “smooth” a phrase sounds and instead focus on whether it accurately reflects the logical connection between the ideas.
Hints
Focus on the relationship between the methods
Ask yourself: is satellite altimetry another detail about echo sounding, an example of echo sounding, a result of echo sounding, or a different method being compared to it?
Pay attention to the limitation mentioned
The passage says echo sounding leaves "vast spaces between survey lines unresolved," but satellite altimetry lets researchers infer features "over wide areas." What kind of relationship is that—similarity, contrast, cause/effect, or example?
Classify each transition type
Think about what each option usually signals: Which one shows a result, which one introduces an example, which one adds a similar point, and which one compares differences?
Step-by-step Explanation
Understand what the first sentences are saying
Read the setup carefully:
- Echo sounding is an older method used to map the ocean floor.
- It gives accurate depth readings directly under a vessel.
- However, it "leaves vast spaces between survey lines unresolved" (a clear limitation/problem).
So we have an older technique with a specific drawback: it does not cover wide areas well.
Understand what the sentence after the blank is doing
Now read the sentence starting at the blank:
"______ satellite altimetry measures slight variations in sea-surface height that correspond to features on the ocean floor, enabling researchers to infer bathymetry over wide areas."
This sentence introduces satellite altimetry, a different technique. It highlights that this method lets researchers infer seafloor features over wide areas, which is exactly what echo sounding struggles with. So the new sentence is presenting an alternative that solves or contrasts with the previous limitation.
Identify the logical relationship between the two ideas
Compare the two methods:
- Echo sounding: accurate under the vessel but leaves many areas unmapped.
- Satellite altimetry: allows inference of seafloor features over wide areas.
The second idea is not a result of the first, not an example of echo sounding, and not just another similar point. It is a different, contrasting approach with an opposite strength (wide coverage vs. gaps). So the needed transition must show contrast between two methods.
Match the relationship to the correct transition word
Now classify the answer choices:
- "Consequently," = as a result (cause/effect)
- "For instance," = for example (gives an example of something just mentioned)
- "Moreover," = in addition (adds a similar or supporting point)
- "By contrast," = on the other hand, in comparison (shows a difference between two things)
We already saw that the passage is contrasting the limitations of echo sounding with the advantages of satellite altimetry, so the transition that explicitly signals this contrast is "By contrast,".