Drill 27 · Reading & Writing · Hard Command of Evidence
SAT R&W Command of Evidence (Hard) — Drill 27 is a Reading & Writing practice drill covering Hard Command of Evidence. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.
These items turn on how a flying insect is held aloft and steered, and on what kind of evidence settles a dispute about a measured effect. The data items, a line graph and a table, reward reading for a difference between two conditions rather than for either curve on its own. The finding items ask which single observation tells two rival causes apart, so weigh each choice for what it actually rules in or out.
In a wind-tunnel study, two model wings are beaten at a range of stroke frequencies and the lift each produces is recorded. One wing is rigid; the other has a flexible trailing edge that bends under load. Both begin at the same low lift at the slowest beat. The question is which wing turns added beat frequency into added lift more effectively, so the researchers compare how steeply each wing's lift climbs as the beat speeds up, not merely which wing ends higher.
Question 1. Which statement best identifies which wing converts faster beating into lift more effectively?
Explanation: Correct: From a shared start, the flexible wing's curve rises faster than the rigid wing's, so the gap between them grows as the beat quickens. A steeper lift-versus-frequency slope is exactly what "converts beating into lift more effectively" means. A: That the rigid wing makes some lift at the slowest beat is true from the graph but describes one point, not which wing gains lift faster as beating speeds up. B: Both curves do rise with frequency, but that they share a direction says nothing about which one rises more steeply. D: The rigid wing making more lift at the highest beat than at the lowest is true of nearly any rising curve; it does not compare the two wings' rates of gain.
On warm mornings a population of dragonflies builds up ground speed after takeoff -- as recorded by a fixed camera -- noticeably faster than on cool mornings. A researcher proposes that the warmth itself is the cause: warmer flight muscle contracts more quickly, so the wings beat faster and the insects pick up speed sooner. The claim treats temperature as acting through the muscle. Before accepting it, the team considers whether some other difference between warm and cool mornings could be driving the quicker gain in ground speed instead.
Question 2. Which finding, if true, would most weaken the proposal that warmer muscle is what makes the dragonflies build up ground speed faster?
Explanation: Correct: The proposal runs through the wingbeats: warmer muscle is supposed to beat the wings faster. If high-speed video shows the wingbeat frequency is no higher on warm mornings, and the quicker gain in ground speed tracks a tailwind instead of appearing on calm warm mornings, then the camera's speed difference is coming from the wind carrying the insects along, not from quicker beats. That cuts the proposed muscle-to-wingbeat pathway directly. B: A feeding effect that holds regardless of temperature is a separate factor; it does not explain why warm mornings in particular bring a quicker gain in ground speed. C: Basking is how the insects warm up, so it fits the muscle-warmth account rather than weakening it. D: Confirming that warmer muscle contracts faster supports the proposal; it does not weaken it.
Behind the wings of a hoverfly sit a pair of tiny club-shaped organs that beat as the insect flies. A researcher proposes that these organs act as motion sensors, detecting when the body begins to rotate off course so the fly can correct mid-air. If that is their job, the researcher reasons, then gently loading them with a trace of added weight to garble their signal should leave brief straight flight in calm air largely intact while making it hard for the fly to recover from a sudden turn. The team designs a test to check that prediction.
Question 3. Which result would best fit the prediction that follows from the motion-sensor proposal?
Explanation: Correct: The proposal predicts a specific split: steady flight should survive but turn-recovery should fail. Loaded flies that still fly straight in calm air yet cannot right themselves after a gust match that prediction exactly, pointing to a rotation-sensing role. A: If loading the organs leaves turn-recovery unharmed, the prediction fails; slower flight alone does not point to a rotation sensor. B: Being unable to take off at all is a gross failure that would implicate basic flight machinery, not the fine course-correction the proposal is about. C: This tests flies with the organs intact, so it cannot show what the organs do; the prediction is about what happens when their signal is garbled.
Table: wingbeat frequency by body mass across four bee species
Across flying insects, heavier bodies tend to beat their wings more slowly. A team measures four bee species that differ in body mass and records each one's typical wingbeat frequency. The three lightest species are shown; the heaviest species' row is left for you to complete. If the usual relationship holds, the heaviest bee should extend the falling trend the lighter three already trace, beating its wings more slowly than any of them.
Question 4. Which value, entered for the heaviest species, would best continue the pattern the lighter three species establish?
Explanation: Correct: From lightest to heaviest the shown frequencies fall: 230, 195, 165 beats per second as mass rises. Continuing that downward trend, the heaviest bee should beat slower than 165, and 130 is the only option that does so. A: 235 is higher than every lighter species, reversing the falling trend instead of continuing it. C: 190 sits between the second and third species' values, so it would put the heaviest bee mid-pack rather than below all three. D: 205 is above all but the lightest species, again breaking the steady decline the lighter three establish.
Foraging ants from one colony travel a reliable path between the nest and a feeding site. One account holds that each ant learns the route from landmarks it sees along the way. Another holds that the ants simply follow a chemical trail their nestmates have laid down, with no learned map involved. Both accounts predict a steady, well-used path, so a researcher arranges a manipulation that the two accounts answer differently.
Question 5. Which result would most strongly support the chemical-trail account over the learned-route account?
Explanation: Correct: Erasing a chemical trail with solvent should wreck trail-following but leave a landmark-learned route intact. The ants losing the path right where the cloth passed, and recovering only once the trail is re-laid, is the signature of trail-following and tells it apart from a learned map. A: Faster travel with repetition could come from a firming chemical trail or from practice on a learned route, so it fits both accounts and separates neither. B: Path unchanged after moving landmarks argues against the landmark-learning account, but it points only weakly toward a trail; ants could navigate by other cues. The solvent test bears on the trail directly. D: Foreign ants ignoring the path is expected under either account, since a colony's own route or its own trail would not serve outsiders; it does not decide between them.