2025 CSAT — Q3
Passage
The history of renewable energy suggests there is a steep learning curve, meaning that, as more is produced, costs fall rapidly because of economies of scale and learning by doing. The firms’ green innovation is path-dependent: the more a firm does, the more it is likely to do in the future. The strongest evidence for this is the collapse in the price of solar energy, which became about 90% cheaper during the 2010s, repeatedly beating forecasts. Moving early and gradually gives economies more time to adjust, allowing them to reap the benefits of path-dependent green investment without much disruption. A late, more chaotic transition is costlier.
Which one of the following statements best reflects the central idea of the passage?
Thinking pathway
Locate. This asks for the central idea, and for an explanatory passage that means reading to the last move — these passages put the mechanism first and the consequence last, and the central idea is the consequence the author built toward, not the machinery. So skip past the learning-curve / path-dependence setup and the solar evidence, and land on the payoff: “Moving early and gradually gives economies more time to adjust… A late, more chaotic transition is costlier.” That payoff is the anchor.
Test (thesis-vs-detail + scope-fit). Ask of each option: is this the machinery or the message? The message is about when you move — early vs. late. (d) “timing plays a crucial role” names exactly that consequence. The others name parts of the machinery or drift the scope.
Eliminate by anatomy. (a) offers a supporting detail as if it were the main point — it lifts a real passage phrase (“economies of scale”) that is one named mechanism inside the explanation and dresses it as the point. (b) is a claim the passage never actually makes — it over-generalises to “modern technological progress” at large when the passage is about green-energy transition specifically. (c) is also a claim the passage never actually makes — it swaps the passage’s “early-moving” for “large,” a claim the text never makes. The recurring lesson: on explanatory RC, distractors are usually true phrases from the passage re-cast as the thesis — distinguish the machinery from the message. Key: (d).
Evidence in the text
“Moving early and gradually gives economies more time to adjust… without much disruption. A late, more chaotic transition is costlier.” The passage’s payoff sentences make when you move (early vs. late) the decisive factor.
Worked rationale
Walk the passage to its payoff. It opens with the learning-curve and path-dependence mechanism, gives solar’s 90% price collapse as evidence, and then lands on the consequence: moving early and gradually is cheap and smooth, while a late transition is costlier. The mechanism (economies of scale, path-dependence) is the why; the central idea is the so-what — timing is decisive.
(d) “Timing plays a crucial role in green technology development” is precisely the passage’s conclusion.
Answer: (d).
Why the other options miss
- A a supporting detail offered as the main point: “economies of scale” is one named mechanism inside the explanation, not the central idea. A supporting detail dressed as the thesis.
- B a claim the passage never actually makes: over-generalises to “modern technological progress” at large; the passage is specifically about renewable/green energy transition, not technology generally.
- C a claim the passage never actually makes: the passage never says large economies adopt green tech better — it says early-moving economies adjust better. Swaps “early” for “large,” a different claim.
Specialist insight
On a central-idea question, the trap options are usually real phrases lifted from the passage (economies of scale, path-dependence) re-cast as the main point — a detail dressed up as the thesis. The scoring move is to read to the passage’s last move: explanatory passages put the mechanism first and the consequence last, and the central idea is the consequence the author built toward. Here every sentence is in service of “early and gradual beats late and chaotic” — i.e. timing. Distinguish the machinery from the message.
(a)/(b) lift real passage phrases (economies of scale, technological progress) as the thesis, but the passage's payoff is timing — (d).