Question 156·Hard·Inferences
Botanist Amara Cho compared pollen profiles extracted from two adjacent lakebeds that recorded vegetation changes over the last 6,000 years. She found that roughly 2,800 years ago the proportion of agricultural grass pollen in both samples doubled, while old-growth oak pollen sharply declined—a pattern that persisted for nearly a millennium before gradually reverting to earlier levels. Charcoal particles, a common proxy for wildfire, did not increase during this interval, and regional climate records reveal no significant shifts in temperature or precipitation.
Taken together, Cho argues, the data indicate that _____
Which choice most logically completes the text?
For “Which choice most logically completes the text?” questions, restate what the missing sentence must do (here: draw a conclusion that fits all evidence). Then use the passage’s constraints—especially negatives like “did not increase” and “no significant shifts”—to eliminate answers that conflict with the record or add unsupported specifics. Finally, pick the option that explains the main pattern (agricultural pollen up, oak pollen down) with the fewest assumptions.
Hints
Use the phrase before the blank
The sentence before the blank says, “Taken together, Cho argues, the data indicate that…”. Ask yourself: What conclusion best fits all the data (pollen, charcoal, climate records) described in the passage?
Pay attention to what did not change
The passage tells you that charcoal did not increase and that regional climate records show no significant shifts. How does that affect answer choices that rely on changes in wildfire or climate?
Notice the kind of plants involved
The pollen that increased is from agricultural grasses, while old-growth oaks declined. What kind of activity usually causes more agricultural plants and fewer old-growth trees in an area?
Watch for unsupported causes
Look for answer choices that introduce specific causes (for example, certain organisms or measurement artifacts) that the passage doesn’t provide evidence for. Those are often traps because they go beyond the information given.
Step-by-step Explanation
Restate the key evidence
Focus on what the data show:
- Around 2,800 years ago, agricultural grass pollen doubled.
- At the same time, old-growth oak pollen sharply declined.
- This pattern lasted for about 1,000 years, then gradually went back toward earlier levels.
- Charcoal particles did not increase, so there’s no evidence of a wildfire spike.
- Climate records show no significant changes in temperature or precipitation.
The blank comes after “Taken together, Cho argues, the data indicate that…,” so the correct ending must be a conclusion that fits all of this evidence.
Identify what causes are disfavored by the passage
The passage explicitly makes two major drivers unlikely:
- Climate shifts in temperature/precipitation: the passage says there were “no significant shifts in temperature or precipitation.”
- More wildfire: charcoal (a proxy for wildfire) did not increase.
So the best conclusion should not depend on a big change in rainfall/temperature or on a documented increase in fire.
Infer the most likely remaining cause
With climate and wildfire not showing notable shifts, the strongest remaining explanation must account for both:
- A big rise in agricultural grass pollen, and
- A big drop in old-growth oak pollen over many centuries.
A sustained increase in agricultural plants is most consistent with human land use (clearing forests and cultivating grasses/crops).
Match your inference to the answer choices
Choose the option that (1) explains the simultaneous rise in agricultural pollen and fall in oak pollen, and (2) aligns with the passage’s point that climate and wildfire do not show major changes.
The best match is: a human-driven expansion of agriculture, rather than climate changes or wildfire, most plausibly explains the long-term reduction of oak pollen beginning 2,800 years ago.