Central Ideas questions give you a short passage (25–150 words) and ask which choice “best states the main idea of the text.” The main idea is the claim the rest of the passage exists to support — not the most interesting detail, and not a lesson beyond the text. The four wrong options are engineered from exactly four traps, so the fastest route is to know the traps by name and eliminate by scope.
How the question announces itself
“Which choice best states the main idea of the text?” — the classic formula.
“According to the text, …” — the detail variant: same skill, narrower target.
Passages are informational summaries (science, history, social science) or short literary excerpts.
The method
Find the load-bearing sentence. One sentence carries the claim; the others give evidence, method, or color. In research passages it is usually the finding (“led the team to conclude…”); in literary passages, the situation the details keep returning to.
State the idea yourself before reading the options. One sentence, your words, including both the subject and what the passage actually says about it. This is your measuring stick — options are compared against it, not against each other.
Eliminate by scope, using the trap names. For each option ask: does it say more than the text (too broad), less than the text (too narrow — a detail), something the text never says (outside), or the opposite (contradiction)? Exactly one option survives all four tests.
The named mistakes behind every wrong answer
Too broad
An option that generalizes beyond the passage — “coastal ecosystems matter more than forests” when the text compared only sediment carbon. True-sounding is not text-supported.
Too narrow
A real detail from the passage promoted to main idea — the method, one measurement, one example. Details support the idea; they are not the idea.
Plausible but absent
A reasonable claim the passage never makes. If you cannot point at the sentence that says it, it is not the answer.
Contradiction
The reverse of what the text says — planted for students who skim. Slower reading of the key sentence eliminates it for free.
Try one
Question 1 — Central Ideas and Details (easy)
Marine ecologist Beatriz Camargo and her team extracted sediment cores from seagrass meadows along three coastlines. Although the meadows cover only a small fraction of the seafloor, the cores revealed that their sediments hold carbon at densities far exceeding those of most forest soils — a finding that led the team to describe seagrass meadows as disproportionately important carbon stores.
Which choice best states the main idea of the text?
Coastal ecosystems are more effective than forests at slowing climate change.
Camargo's team found that seagrass meadows store carbon at unusually high densities despite covering little of the seafloor.
Camargo's team collected sediment cores from seagrass meadows along three coastlines.
Seagrass sediments hold less carbon than most forest soils do.
Answer: B. The text builds to the finding that seagrass sediments hold carbon at densities exceeding most forest soils despite the meadows' small area — the 'disproportionately important' conclusion.
The full Central Ideas & Details lesson inside Satisfied adds detail-variant drills, literary passages, and timed sets that train the scope test until it is automatic.