Question 56·Medium·Central Ideas and Details
Ecologist Maya Fernandez notes that the long-lived bristlecone pine preserves a climate record stretching back millennia. By measuring the width and chemical composition of each annual growth ring, Fernandez and her team reconstructed temperature and precipitation patterns as far back as 2500 BCE. They discovered, for example, that a surge in tree growth during the eighth century CE aligned with unusually wet summers, whereas a series of narrow rings in the twelfth century corresponded to a severe drought described in Indigenous oral histories. Fernandez argues that these dendrochronological findings can refine modern climate models by offering concrete evidence of how regional ecosystems have responded to past extremes.
Which choice best expresses the main idea of the text?
For main-idea questions, read the entire passage or paragraph, then focus on the first sentence (often the topic) and the last sentence (often the conclusion or claim). Ask yourself: “If I had to summarize what the author is doing in one sentence, what would it be?” Then eliminate answers that focus on a single example, a side detail, or an exaggeration not supported by the text, and choose the option that matches the overall purpose and scope of the passage.
Hints
Look at the first and last sentences
Reread the first and last sentences of the paragraph. What big idea do they introduce and then come back to?
Separate main idea from examples
Ask yourself: Which parts of the paragraph are specific examples, and which part states what Fernandez is ultimately claiming about her research overall?
Check the scope of each answer choice
For each option, ask: Does this describe the entire paragraph, or just one detail or event mentioned in it?
Step-by-step Explanation
Identify what the whole passage is about
Read the paragraph and ask: What is the general topic? Here, the text is about ecologist Maya Fernandez using bristlecone pine tree rings to study past climate (temperature and precipitation) over thousands of years.
Notice how the examples are used
The middle of the passage gives specific examples:
- A surge in tree growth in the eighth century matches unusually wet summers.
- Narrow rings in the twelfth century match a severe drought described in Indigenous oral histories.
These are supporting details. They show how the tree-ring data lines up with known climate events, but they are not the main idea themselves.
Focus on the author’s overall claim
Look closely at the first and especially the last sentence:
- The first sentence introduces tree rings as a climate record stretching back millennia.
- The last sentence says these dendrochronological findings can refine modern climate models.
Together, these show that the main point is about using long-term tree-ring climate records to improve present-day climate modeling, not about any one specific event or comparison.
Match the main idea to the best answer choice
Now compare this overall idea to the options:
- Choices B and C focus on single examples from the middle of the paragraph, so they are too narrow.
- Choice D makes a strong claim about the twelfth-century drought being the worst in 5,000 years, which the passage never states.
- Choice A summarizes the full point: tree-ring analysis provides valuable historical climate information that can improve modern climate models.
So, the best answer is A) Tree-ring analysis can supply valuable historical climate information that improves present-day climate models.