Question 104·Medium·Central Ideas and Details
Marine biologist Aisha Khan and colleagues at the Pacific Research Institute have discovered that when certain species of coral are paired with a heat-tolerant strain of symbiotic algae, the coral can survive water temperatures 1.5 °C higher than usual without bleaching. The team’s three-year field experiment across several reef sites suggests that corals can naturally acquire these algae from their surroundings, but only when local water quality is high and stressors such as pollution are minimized. Khan argues that conservation efforts should prioritize reducing coastal pollutants to foster conditions that let corals strengthen themselves against rising temperatures.
Which choice best states the main idea of the text?
For main idea questions, first ignore the choices and quickly summarize the passage in 1–2 simple sentences that combine what the researchers found with any recommendation or conclusion given, especially in the last sentence. Then eliminate choices that (1) focus on only one detail, (2) introduce new claims not in the passage (like extreme comparisons or settings), or (3) contradict key facts. Choose the option that best matches your own summary in scope and emphasis, without adding or exaggerating anything.
Hints
Restate the passage briefly
Before looking closely at the choices, try to say in one short sentence what the entire passage is mainly about, including both what the study found and what Khan recommends.
Use the beginning and the end of the passage
Look at how the passage begins (what the researchers discovered) and how it ends (what Khan argues should be done). How are these two parts connected?
Watch for answer choices that go beyond the text
Check each option for words that add extra claims, like direct comparisons ("greater than"), absolute limits ("only"), or settings ("laboratory") that the passage never mentions or supports.
Link cause and effect
Think about what conditions the study says are necessary for the corals and algae, and what effect those conditions have on the corals’ ability to handle warmer water.
Step-by-step Explanation
Clarify what the question is asking
The question asks: "Which choice best states the main idea of the text?" This means you must identify the overall point of the entire passage, not just a single detail or example.
Summarize each sentence in your own words
Go sentence by sentence:
- First sentence: Khan’s team found that when some corals are paired with heat-tolerant algae, they can survive water that is 1.5 °C warmer without bleaching.
- Second sentence: Their three-year field experiment suggests corals can naturally pick up these algae from their surroundings, but only when water quality is good and pollution and other stressors are low.
- Third sentence: Because of this, Khan says conservation should focus on reducing coastal pollution so conditions allow corals to strengthen themselves against rising temperatures.
Combine the ideas into one central message
Now put the sentence summaries together: the study is about how corals can naturally gain heat-tolerant algae if water quality is high, and based on that, Khan recommends focusing conservation on reducing pollution so corals can better handle warmer oceans. The correct answer must reflect both the scientific finding (natural partnership with heat-tolerant algae, dependent on good water quality) and the implication for conservation (improving water quality to help corals resist warming).
Match the combined main idea to the best answer choice
Check each option against your combined summary. Only choice B) "Khan’s study shows that improving water quality enables corals to naturally partner with heat-tolerant algae, boosting their resilience to warming seas" includes all key parts: the role of water quality, natural acquisition/partnership with heat-tolerant algae, and increased resilience to higher temperatures. Therefore, B is the correct answer.