Question 157·Medium·Central Ideas and Details
Marine biologist Leila Santoro and her colleagues recently used long-lasting acoustic transmitters to monitor the movements of bluntnose sixgill sharks, a deep-sea species that rarely surfaces. Contrary to prevailing assumptions that the sharks remain at moderate depths year-round, the team found that many individuals migrate each winter to ocean trenches more than 2,500 meters deep, remaining there for months before returning to the continental shelf. Santoro argues that this seasonal dive suggests the sharks are exploiting an unrecognized food source and that deep trenches may be far more ecologically active than previously believed.
Which choice best describes the central finding of the study?
For central-idea questions about a study, first identify the sentence or two that directly state what the researchers "found," "discovered," or "observed." Then separate that result from (1) background context, (2) methods or tools, and (3) interpretations, implications, or opinions. Check each answer for strict alignment with the passage’s stated result, quickly eliminating choices that: focus on methods instead of findings, introduce new causes or consequences not mentioned, or alter key details like time, place, or quantity. This targeted reread keeps you from being distracted by interesting but secondary details.
Hints
Find where the result is stated
Look for the part of the passage where it says what the team "found" or what happened with the sharks, rather than how the study was done.
Distinguish result from method and opinion
Identify which sentences describe the research method (what tools they used), which give the concrete result, and which give Santoro’s interpretation or argument about that result.
Watch for added or changed details
When you read each answer choice, ask: Does the passage actually mention that specific detail (like a season, location type, or cause), or is the answer adding something new that isn’t stated?
Connect to the challenge to prior beliefs
Notice how the passage contrasts "prevailing assumptions" with what the team found. The correct answer should reflect both the new pattern and how it goes against earlier ideas.
Step-by-step Explanation
Identify what the question is really asking
The question asks for the central finding of the study. That means you need the main result of the research—what the scientists actually discovered—not background information, not how they did the study, and not broader consequences or opinions.
Locate the sentence that states the study’s result
Scan the passage for where it directly tells you what the team found or discovered. The key sentence is: "Contrary to prevailing assumptions that the sharks remain at moderate depths year-round, the team found that many individuals migrate each winter to ocean trenches more than 2,500 meters deep, remaining there for months before returning to the continental shelf." This sentence gives the concrete result of the tracking.
Separate the finding from methods and interpretations
Notice that:
- The methods are described in "used long-lasting acoustic transmitters to monitor the movements..." That tells how they studied the sharks, not what they found.
- The finding is the new movement pattern described in the "team found that..." sentence.
- The interpretation/implication comes later: "Santoro argues that this seasonal dive suggests..." That is what the finding might mean, not the finding itself. For the central finding, focus on the new movement pattern and how it contradicts earlier assumptions.
Match each answer choice to the actual finding
Now compare each option with the sentence stating the result:
- Choice A talks about sharks in shallow coastal waters during summer months, which is never mentioned; the passage describes deep ocean trenches in winter.
- Choice C introduces declining numbers and overfishing, which are not in the passage at all.
- Choice D focuses on the technology’s battery life, which is only hinted at by "long-lasting" and is not presented as the main result.
- Choice B captures that the study found a regular (yearly) migration to very deep trenches and that this finding challenges earlier assumptions about where the sharks stay and how active deep trenches are. Therefore, the best description of the central finding is: The study discovered a yearly migration of bluntnose sixgill sharks to very deep ocean trenches, challenging assumptions about deep-sea habitats.