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SAT Reading & Writing: Hard Inferences (Drill 21)

Drill 21 · Reading & Writing · Hard Inferences

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About This Drill

SAT Reading & Writing: Hard Inferences (Drill 21) is a Reading & Writing practice drill covering Hard Inferences. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.

These hard SAT inference questions ask you to complete short academic passages by choosing the conclusion the text best supports. The right answer stays inside the evidence; the wrong ones tend to overreach, reverse the logic, or wander off the passage's point.

Questions & Explanations

Text
A geologist examines a thin shale bed exposed in a road cut and finds it packed with the shells of a single-celled plankton species. That species is well known from the fossil record: it appears nowhere in older rocks and shows up abruptly at a horizon that other sections have tied to a specific dated ash layer, after which it becomes common. Nothing in the bed's minerals or shells suggests the fossils washed in from elsewhere; they lived and were buried where they now sit. Because a rock cannot contain a creature that had not yet come into being, the shale bed ______

Question 1. Which choice most logically completes the text?

  • A) must be older than that first-appearance horizon, because rock crowded with well-preserved fossils has generally had the longest time to gather them.
  • B) must be no older than the horizon where that plankton first appears, since the shale holds a species that did not exist in earlier times. ✓
  • C) can be dated to the exact year of the ash layer, since the plankton it contains pins the bed to that single moment.
  • D) most likely formed in far deeper water than the ash layer did, given how densely the tiny plankton shells are packed together.

Explanation: (B) The plankton appears in no older rocks and turns up abruptly at a dated horizon, and the shells were buried where the animals lived, so the bed cannot predate the moment that species came into being; it is therefore no older than that first-appearance horizon. The choice states exactly that oldest-possible bound. (A) makes the bed older and reads its dense fossils as long accumulation, but a species' first appearance caps how old a bed containing it can be. (C) claims a precise year, yet a first-appearance datum fixes an order, not a date. (D) guesses at water depth the passage never raises.

Text
Along one rocky shore, biologists first explained the unusually thick shells of a tide-pool snail entirely by the presence of shell-crushing crabs, whose scent is known to prompt snails to lay down heavier armor. A wider survey unsettled that tidy account. Snails living on the most wave-battered outcrops grew shells just as thick even where crabs were scarce, and thickness rose steadily with exposure to pounding surf, which itself favors a sturdier shell. Crab scent and heavy wave action overlap along this coast, and the survey cannot tell how much each contributes to any one population's armor. Given that two influences are tangled in the snails' surroundings, the thick shells ______

Question 2. Which choice most logically completes the text?

  • A) are due mostly to crab scent, with the pounding surf adding only a small and secondary amount to their thickness.
  • B) show that crab scent plays no part at all, since thickening on this shore comes from wave exposure rather than any predator cue.
  • C) cannot be traced to crab scent alone, since shells grew just as thick on wave-battered rocks where crabs were scarce. ✓
  • D) probably reflect a difference in the seawater's mineral content between the more exposed pools and the sheltered ones.

Explanation: (C) Snails on the most wave-battered rocks grew equally thick shells even where crabs were scarce, and thickness tracked surf exposure, so heavier armor cannot be pinned on crab scent by itself; wave action is an equally live cause the data cannot rank against it. The choice revises the crab-only account without denying that crab scent contributes. (A) makes crab scent the main driver, but the survey cannot tell how much either factor contributes, so ranking them overreaches. (B) denies crab scent any role, which contradicts the stated fact that its scent prompts heavier shells. (D) invents a mineral difference the passage never mentions.

Text
A bookstore chain noticed that new membership sign-ups climbed sharply at one branch over a single spring. That spring the branch had added an in-store coffee bar, and the manager wondered whether the coffee bar pulled in the new members or whether reading in general was simply having a good season across the region. The chain checked a second branch of similar size and neighborhood that had added no coffee bar over the same weeks. There, sign-ups held flat, showing none of the climb seen at the first branch. Because only the branch with the new coffee bar saw sign-ups rise, the coffee bar ______

Question 3. Which choice most logically completes the text?

  • A) is a more plausible driver of the sign-up climb than a broad seasonal rise in reading, since only that branch climbed. ✓
  • B) plainly had nothing to do with the climb, since sign-ups had already been rising steadily at both branches well before that spring.
  • C) most likely mattered far less than the branch's own decision to extend its evening hours over those same spring weeks.
  • D) drew the new members chiefly because the comparison branch sat in a distinctly wealthier neighborhood with more casual foot traffic.

Explanation: (A) Sign-ups rose only at the branch that added the coffee bar, while a matched branch with no coffee bar stayed flat over the same weeks, so a region-wide good season for reading cannot explain a climb that appeared in just one place, and the coffee bar better fits the pattern. The choice ties the rise to the coffee bar without calling it the only cause. (B) says sign-ups had been climbing at both branches, contradicting the flat record at the comparison branch. (C) credits an evening-hours change the passage never mentions. (D) blames a neighborhood wealth gap, but the branches were matched on neighborhood, so that was held constant.

Text
To census the bats using a limestone cave, a survey team recorded a single night with a detector set to log calls in one narrow band of frequencies, then reported the tally as the cave's bat community. The detector caught many passes and identified several species quickly. But bats do not all echolocate in the same range: some species call well above the band the detector was set to record, and their calls would never have registered on it, however many of those bats streamed past. Because the survey could only hear species calling within its single recording band, its picture of the cave's bats ______

Question 4. Which choice most logically completes the text?

  • A) proves that only the species it logged make any real use of the cave as a roosting and feeding site.
  • B) is useless for any purpose, because a survey run with one detector can never be set beside a survey run with another.
  • C) probably overstates the total, because a single night of recording is far too short to sample a cave community fairly.
  • D) likely leaves out species that call above the recorded band, since their echolocation could not have registered on the detector at all. ✓

Explanation: (D) The detector logged only calls within one narrow band, and species that echolocate above that band could not register on it no matter how many passed, so a tally built from the recorded band cannot stand for the whole community; the choice names that frequency gap. (A) treats the logged species as the cave's only real users, but the others were merely unheard. (B) calls the result useless and incomparable, overstating a fixable coverage limit. (C) blames the single night, yet the flaw is the recording band; more nights in the same band would still miss the high-frequency callers.

Text
On one common account of dramatic irony, the effect arises only when the audience knows something that a character on stage does not, so that the audience watches the character act in the dark; where the audience and the character possess exactly the same knowledge, the account holds, no dramatic irony can occur. Consider a scene in which a messenger reveals a secret to a character at the very moment the audience learns it too, leaving the two equally informed from then on. If the account is right, a reader applying it to this scene should conclude that the scene ______

Question 5. Which choice most logically completes the text?

  • A) achieves dramatic irony especially strongly, because letting the audience and the character learn a secret together binds them in shared suspense.
  • B) does not generate the dramatic irony the account defines, since the audience and the character come to know the secret at the very same moment. ✓
  • C) cannot be assessed by the account at all, since a scene built around a spoken revelation lies outside what the account was meant to cover.
  • D) still counts as dramatic irony on the account, given that any scene withholding a secret until a late reveal satisfies what the account asks for.

Explanation: (B) The account makes dramatic irony depend on the audience knowing something a character does not, and here the messenger's reveal leaves audience and character equally informed from the same moment on, so the required gap in knowledge never opens and the effect the account defines cannot arise. The choice applies the rule as stated. (A) says learning together heightens the irony, but the account requires the audience to know more, so it reverses the standard. (C) places the scene outside the account, yet the account exists to judge just such cases. (D) claims a late reveal satisfies the account, but a reveal shared with the audience creates no knowledge gap.