Drill 29 · Reading & Writing · Hard Command of Evidence
SAT R&W Command of Evidence (Hard) — Drill 29 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.
A glacier records its own history in ice, debris, and the marks it leaves on the land, and these items ask which trace decides between rival causes of a change. The finding items reward weighing what each observation can and cannot rule out. The two data items, a table and a line graph, are built to be read for a difference between two responses rather than for a single number.
A low ridge of jumbled rock and sediment runs across a valley below the snout of a glacier. One reading is that the glacier pushed the ridge up as it advanced, bulldozing loose material ahead of its leading edge. Another is that the ridge marks where the ice front paused during a long retreat, dropping debris in place as it melted back. The ridge's bulk fits either story, so a glaciologist examines how the material inside it is arranged.
Question 1. Which finding, if true, would most strongly support the bulldozed-by-advance reading over the dropped-in-retreat reading?
Explanation: Correct: Advancing ice shoves and crumples the material it pushes, so folded, steeply tilted layers facing the glacier are the telltale mark of bulldozing. Debris merely dropped as ice melted back would settle in looser, undisturbed layers, so the deformation tells the two readings apart. A: Up-valley rock types show only that the glacier carried material from above; ice transports debris whether it is advancing or retreating, so this does not separate the two. C: That this ridge is taller than a lower one compares two ridges but says nothing about whether this one was pushed up or dropped in place. D: Lichen on the crest speaks to how long the boulders have been exposed, not to how the ridge was built.
Table: four glaciers measured over different spans
A survey compares four glaciers by how fast they are thinning. The table lists, for each glacier, the total thickness it lost and the number of years over which that loss was measured. A scientist wants the glacier thinning fastest -- the most thickness lost per year -- rather than the one with the largest total loss, since a glacier measured over many years can pile up a big total simply by being watched longer. Answering means dividing each glacier's total loss by its number of years and comparing the rates.
Question 2. Based on the table, which glacier is thinning fastest per year?
Explanation: Correct: Dividing loss by years gives the yearly rate: Glacier C lost 24 meters over 6 years, or 4.0 meters per year, the fastest of the four (A is 2.0, B about 2.7, D 3.0). C thins fastest per year even though its total loss is not the largest. A: Glacier A has the largest total loss (40 meters), but spread over 20 years that is only 2.0 meters per year, the slowest rate of the four. B: Glacier B lost 30 meters over 11 years, about 2.7 meters per year -- more than A but below C's 4.0. D: Glacier D's rate is 15 over 5, or 3.0 meters per year -- second fastest, but still short of C's 4.0.
A broad slab of bedrock in a valley floor bears a set of fine, parallel scratches. Two interpretations compete. On one, a glacier ground across the slab, dragging embedded rock fragments that scored the parallel grooves as the ice flowed down-valley. On the other, a single landslide swept a sheet of debris across the slab and scratched it in passing. The bare grooves fit either event, so a geologist looks for a feature that one process would leave and the other would not.
Question 3. Which finding, if true, would most strongly favor the glacier interpretation over the landslide interpretation?
Explanation: Correct: A single local landslide would not normally produce the same aligned scratch direction repeated across many separated bedrock surfaces strung along the whole valley. That valley-long, consistently aligned pattern is what a glacier flowing the length of the valley would leave, which is what tells the glacier reading apart from a slide. B: Varying scratch depth on one slab reflects differences in the fragments doing the scoring; both a glacier and a landslide would drag a mix of sizes, so it does not separate them. C: Loose debris nearby is consistent with either a glacier's deposit or a landslide's, so it favors neither. D: That the rock holds a scratch explains why grooves survived at all; it says nothing about which process cut them.
Two neighboring glaciers are tracked through a melt season as air temperature climbs. One sits in a sun-exposed basin; the other lies under the shadow of a high ridge for much of the day. Both begin the season losing very little. The researchers want to know which glacier's melt responds more sharply to the warming air, so they compare how steeply each one's cumulative melt rises as the season advances, not merely which ends with more melt.
Question 4. Which statement best identifies which glacier's melt responds more sharply to the warming season?
Explanation: Correct: From a shared low start the sun-exposed glacier's melt curve rises far faster than the shaded one's, so the gap between them grows as the season warms. A steeper cumulative-melt slope is exactly the sharper response to warming that the question asks about. A: Both glaciers melting more as it warms is true but shared, so it does not say which one responds more sharply. C: The shaded glacier losing some ice early describes one stretch of its curve, not how sharply either glacier answers the warming. D: More total melt in the sun-exposed glacier follows from its steeper rise, but a single end-of-season total does not by itself describe the rate of response the question targets.
Drilling into a glacier, a team finds that the annual ice layers laid down over one recent stretch of years are thicker than those from earlier decades. A researcher proposes that snowfall rose over that stretch, since heavier yearly snow would build thicker layers. The claim treats layer thickness as a direct record of how much snow fell. Before accepting it, the team weighs whether something other than snowfall could thicken the layers.
Question 5. Which finding, if true, would most weaken the proposal that thicker layers mean more snow fell during that stretch of years?
Explanation: Correct: If colder firn compacted more slowly over that stretch, each year's layer would settle to a greater thickness even with no extra snow -- a clean rival cause for the thickening. Because the snowfall gauges recorded similar totals for the two periods, slower compaction is left as the difference competing with the more-snow account, which undercuts it. A: Matching dust in thick and thin layers speaks to dust sources, not to whether snowfall or compaction set the layer thickness. B: Year-to-year snowfall varying regionally is general background; it neither explains the sustained thickening nor offers a rival to the snowfall account. C: This removes one possible depth-related confound, which if anything makes the more-snow reading cleaner; it does not offer a rival cause for the thickening.