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SAT Reading and Writing

Central Ideas and Details

Central Ideas and Details is a skill in the Information and Ideas domain of the Digital SAT Reading and Writing section. These are practice questions on it, and each answer choice comes with an explanation of why it is right or wrong.

13 questions. After every answer you’ll see why each choice is right or wrong, not just the one you picked.

Round length
Difficulty (none selected means all)

Sample questions

Open a question to see the answer choices and the correct answer.

When the Erie Canal opened in 1825, it reduced the cost of shipping goods between the Great Lakes region and New York City by more than ninety percent compared to overland transport. This dramatic drop in shipping costs allowed farmers in the Midwest to sell grain profitably in eastern markets for the first time, spurring rapid agricultural settlement across the region and transforming New York City into the young nation's busiest port. Which choice best states the main idea of the text?
  1. A. The Erie Canal was primarily built to help New York City become the nation's busiest port.
  2. B. Overland transport between the Great Lakes and New York City remained more common than canal transport after 1825.
  3. C. Farmers in the Midwest could not sell grain in eastern markets before 1825 due to a lack of demand.
  4. D. By making shipping dramatically cheaper, the Erie Canal reshaped both Midwest settlement and New York City's economic importance. ✓

Correct answer: D. The text traces both effects, agricultural settlement in the Midwest and New York City's rise as a port, back to the canal's dramatic reduction in shipping costs.

Efforts to reintroduce gray wolves to a national park in the 1990s produced an unexpected ripple effect throughout the park's ecosystem. With wolves once again present, elk herds began avoiding open valleys where they were easily hunted, spending more time in wooded areas instead. This shift allowed young willow and aspen trees in the valleys, previously kept short by constant elk grazing, to grow tall enough to stabilize riverbanks, which in turn reduced erosion along the park's streams. According to the text, why did young willow and aspen trees begin growing taller in the park's valleys?
  1. A. Elk spent less time grazing in the valleys after wolves were reintroduced. ✓
  2. B. Park rangers planted new, faster-growing tree species in the valleys.
  3. C. Erosion along the park's streams decreased, which allowed the trees to grow taller.
  4. D. Wolves began eating the young willow and aspen trees directly, which improved the trees' resilience.

Correct answer: A. The text states that elk avoided the open valleys once wolves returned, reducing grazing pressure and allowing the trees to grow taller.

Contrary to the popular image of medieval illuminated manuscripts as the work of solitary monks laboring in silence, many were in fact produced through a coordinated division of labor. One artisan might rule the lines on a page, another might pen the text, and yet another, a specialist illustrator, might add elaborate decorative borders and miniature paintings weeks or months later, sometimes in an entirely different workshop. Which choice best states the main idea of the text?
  1. A. Workshops that produced illuminated manuscripts were located exclusively in monasteries.
  2. B. The creation of medieval illuminated manuscripts often involved multiple specialized workers rather than a single solitary monk. ✓
  3. C. Medieval monks were solely responsible for writing the text of illuminated manuscripts.
  4. D. Illuminated manuscripts were rarely decorated with illustrations or borders.

Correct answer: B. The text's central corrective claim is that manuscript production involved several specialized workers dividing tasks, not a single solitary monk.

Tardigrades, often called water bears, can survive being dried out almost completely, a state in which their metabolism drops to nearly zero and can remain so for years. When rehydrated, most individuals resume normal activity within hours. Researchers have since found that tardigrades produce a unique protein that seems to vitrify, or glass-ify, the cell's interior during desiccation, preventing the structural collapse that dehydration usually causes in other organisms. Which choice best states the main idea of the text?
  1. A. Tardigrades survive extreme drying because a specialized protein protects their cells from collapsing during dehydration. ✓
  2. B. Tardigrades are commonly known as water bears because they require large amounts of water to survive.
  3. C. Most organisms can resume normal activity within hours of being rehydrated after drying out.
  4. D. Tardigrades' metabolism increases dramatically while they are in a dried-out state.

Correct answer: A. Correct — this captures the passage's central claim, that a unique protein prevents cellular collapse and explains how tardigrades endure being dried out for years.

Contrary to the assumption that ancient Rome's roads were built primarily for trade, most of the earliest major roads radiating from the capital were constructed for military logistics: moving legions and supplies quickly to frontier provinces. Trade goods certainly traveled the same roads later, but commercial traffic was a secondary use that grew once the network already existed, not the original design purpose engineers had in mind. According to the text, what was the original purpose of Rome's earliest major roads?
  1. A. to facilitate trade between Rome and its provinces
  2. B. to move military legions and supplies to frontier provinces quickly ✓
  3. C. to connect rural farms to urban markets
  4. D. to allow ordinary citizens to travel between cities for leisure

Correct answer: B. Correct — the passage explicitly states that the earliest major roads were constructed for military logistics, specifically to move legions and supplies to frontier provinces.