Question 134·Medium·Central Ideas and Details
Marine ecologist Dr. Leila Hamdan and her team attach lightweight sensors to small aerial drones, allowing them to skim just above the ocean surface and sample tiny droplets of seawater thrown into the air by waves. Traditional research vessels cannot easily collect these aerosols without contaminating them with ship exhaust, so data on airborne marine microbes have been scarce. By combining drone technology with advanced DNA sequencing, Hamdan is mapping how ocean bacteria travel through the atmosphere and influence cloud formation hundreds of miles inland.
Which choice best states the central idea of the text?
For central idea questions, first summarize the passage in a short sentence in your own words before looking at the choices. Then eliminate any options that (1) focus on a minor detail instead of the overall point, (2) introduce ideas not in the text, or (3) use extreme language the passage doesn’t support (like “entirely” or “primary”). Finally, choose the option that best captures both the main subject and the author’s overall purpose, even if it doesn’t repeat the passage’s exact wording.
Hints
Restate the question in your own words
You are being asked: What is the main point the author wants you to take away from this paragraph? Don’t focus on one sentence—think about the whole passage together.
Find the problem and the solution
What difficulty do scientists face when studying airborne marine microbes, and what new method does Hamdan use to solve that problem? The central idea will connect these two pieces.
Watch out for extreme or overly narrow answers
Eliminate choices that focus on only one detail (like health risks or clouds) or that use extreme words like “entirely” or “primary” in ways the passage does not support.
Check that the answer fits the WHOLE passage
Make sure the choice you pick matches the description of the drones, the contamination issue, and the goal of understanding how bacteria move and affect the atmosphere—not just one of those parts.
Step-by-step Explanation
Identify what the passage is MOSTLY about
Read the whole passage and ask: What is the main focus, not the side details?
The passage introduces Dr. Hamdan, describes how she uses drones with sensors to collect seawater droplets in the air, explains the problem with traditional ships (exhaust contamination), and then mentions using DNA sequencing to map how bacteria travel and affect clouds. Overall, it is mainly about a new way to study airborne ocean microbes and what that makes possible.
Ignore details that are not the central focus
Look for ideas that are mentioned only briefly or as background, and set them aside as main ideas:
- Ship exhaust is mentioned, but only as a limitation of old methods.
- DNA sequencing is mentioned as a tool Hamdan uses, not as the central story.
- Cloud formation is affected by bacteria, but that is one result of the research, not the passage’s main point.
The central idea ties together the problem (contamination from ships) and the solution (drones collecting clean aerosols).
Compare each answer to the passage’s main focus
Now check each option against what you decided is the main idea:
- One option focuses only on the danger of ship exhaust to researchers.
- One makes DNA sequencing the main or “primary” collecting tool.
- One focuses narrowly on bacteria completely determining cloud formation.
- One emphasizes that Hamdan’s drone method offers a new, cleaner way to study airborne ocean microbes.
Ask: Which one best sums up the overall story of the paragraph, including both the problem with ships and the solution using drones?
Choose the answer that captures both the new method and its purpose
The best answer must mention the novel use of drones and the fact that this method avoids contamination, allowing scientists to study ocean microbes in the air more accurately. Only the choice stating that “Hamdan’s use of drones is providing a novel, uncontaminated way to study ocean microbes in the air” captures all of these central points, so that is the correct answer.