Question 144·Hard·Central Ideas and Details
Tree-ring analysis, or dendrochronology, is often praised for its ability to reconstruct past climates with annual precision. Yet this method has significant constraints: many tropical trees produce faint or irregular rings, making dating nearly impossible; at higher latitudes, wood decomposition can erase records older than a few centuries; and matching ring patterns across distant sites requires overlapping samples that are rarely available. Because of these challenges, climate scientists are increasingly turning to complementary tools such as lake sediments and ice cores to fill the gaps left by dendrochronology.
Which choice best states the main idea of the text?
For main-idea questions, first quickly paraphrase the passage in your own words—ask yourself, “Overall, what is the author trying to say?” Then test each answer: eliminate choices that (1) focus on just one detail, (2) exaggerate (use words like ‘always,’ ‘never,’ ‘primary,’ ‘unmatched’ when the passage is more balanced), or (3) contradict any part of the passage. The correct answer will usually reflect both the beginning setup and the final takeaway, and it will match the passage’s tone and scope without going beyond what is stated.
Hints
Use the beginning and end of the passage
Check what the first sentence says about dendrochronology and what the last sentence says scientists are doing. How does the passage move from the beginning to the end?
Notice transition words
Pay attention to the word “Yet” at the start of the second sentence and “Because of these challenges” later. What do these transitions tell you about the author’s main point?
Ask: Is this answer too narrow or too extreme?
For each choice, decide if it only talks about one detail, or if it makes a stronger claim than the passage supports. The best main-idea answer should match the overall message, not just a single example or an exaggeration.
Look for both parts of the idea
The passage both acknowledges dendrochronology’s strengths and emphasizes its problems. Which choice includes both of these aspects?
Step-by-step Explanation
Identify what the first sentence does
Read the first sentence: it says dendrochronology is praised for its precise climate reconstructions. This introduces dendrochronology in a positive way and explains why it is valued.
See how the passage shifts after the praise
Look at the word “Yet” at the start of the second sentence. This contrast shows the passage is moving from positive aspects to problems or limits with dendrochronology.
Summarize the listed problems
The passage gives three specific constraints: tropical trees with faint/irregular rings, wood decomposition erasing older records, and difficulty matching ring patterns across distant sites. All of these support the idea that dendrochronology has important limitations.
Focus on the final sentence (often the main point)
The last sentence explains the consequence of these challenges: scientists are “increasingly turning to complementary tools such as lake sediments and ice cores to fill the gaps left by dendrochronology.” So the main idea combines two parts: dendrochronology is useful, but because of its limits, scientists also rely on other climate records. The choice that best captures this full idea is: While dendrochronology is a valuable tool, its limitations lead researchers to seek other climate records.