Question 119·Medium·Central Ideas and Details
Engineers studying the chiton, a marine mollusk whose teeth are coated with magnetite, believe that the animal’s unusual mouthparts could inspire a new generation of wear-resistant 3-D-printed tools. The chiton grows its teeth continuously, layering nanoscale crystals of iron oxide onto a flexible protein matrix. According to materials scientist Javier Gomez, mimicking that method could allow manufacturers to print drill bits that sharpen themselves as they are used, reducing the need for frequent replacement. While developing a commercial product is still years away, preliminary tests show that synthetic chiton-like composites remain intact after drilling through metal plates that quickly blunt conventional steel bits.
Which choice best states the text’s main idea?
For main-idea questions, read the whole passage or paragraph first, then pause and summarize it in your own words before looking at the choices. When checking options, eliminate those that (1) focus on a single detail or example instead of the big picture, (2) add information or claims not actually stated, or (3) get the timing or certainty wrong (e.g., saying something has been invented when the text only says it could be developed). Choose the option that best matches your summary and covers both what the passage is about and why it matters.
Hints
Think about the whole paragraph
Before looking closely at the options, ask yourself: If I had to tell a friend what this paragraph is about in one sentence, what would I say?
Look at the beginning and the end
Pay special attention to the first and last sentences: what idea do they introduce, and how does the paragraph wrap up that idea?
Check for details vs. main point
Some choices repeat facts from just one sentence. Ask: Does this choice include both what the engineers are studying and why they are studying it?
Watch for information not in the passage
Make sure the answer you pick does not claim something that the passage only suggests as a possibility or never says at all.
Step-by-step Explanation
Identify what the question is asking
The question asks for the main idea of the text. That means you should look for the overall point of the entire paragraph, not just one sentence or an interesting detail.
Summarize the paragraph in your own words
Quickly restate the paragraph:
- Engineers are studying a marine animal (the chiton) whose teeth are coated with magnetite.
- The chiton grows its teeth in a special way (layering iron oxide on a protein matrix).
- A scientist, Javier Gomez, thinks copying this method could let manufacturers 3-D-print drill bits that sharpen as they are used.
- Early tests show these new materials stay intact while regular steel drill bits become dull.
Overall, the paragraph connects the chiton’s unusual teeth to the possible creation of new, more durable drilling tools.
Eliminate choices that are too narrow or factually wrong
Now compare your summary to the answer choices:
- Ask: Does this choice cover the whole paragraph, or just one detail?
- Also ask: Is everything in the choice actually stated or clearly implied by the passage?
You should notice that some options talk only about a specific person, a specific mineral fact, or just one result (like conventional bits getting dull) instead of the broader idea of the animal inspiring tool design.
Match the best overall summary to the text
The only choice that captures the full message—that engineers are studying the chiton’s self-renewing teeth so they can create new, longer-lasting, self-sharpening 3-D-printed drilling tools—is D) The chiton's self-sharpening teeth may guide the design of longer-lasting drilling tools.