SAT central ideas and details questions: how to answer them

Sea otters often float on their backs while they eat, using their chests as tables. To open hard-shelled prey such as clams, an otter may place a flat stone on its chest and strike the shell against it until it cracks. Some otters even keep a favorite stone tucked in a pouch of loose skin under their forelegs.

The following text is from a short story.

Grandpa Ray's workshop smelled of sawdust and oil. Every tool hung on the wall inside its own painted outline, so that a missing hammer left a hammer-shaped gap that accused whoever had borrowed it. Jonah had learned early: you could use anything in the workshop, but you put it back where its shadow waited.

The common image of medieval monasteries as isolated retreats owes much to the writings of the monks themselves, who praised withdrawal from the world. Account books from several monasteries tell a different story. They record wool sold to merchants in distant cities, loans made to local nobles, and payments to masons, glassmakers, and lawyers. Far from standing apart, these communities were deeply woven into the economic life of their regions.

Ancient Roman concrete has survived for two thousand years in harbors where modern concrete would crumble within decades. For a long time, the small white lumps of lime scattered through Roman concrete were dismissed as a sign of careless mixing. Materials scientist Admir Kovač has proposed a different view: when cracks form and water seeps in, the lime lumps dissolve and recrystallize, filling the cracks. What looked like sloppiness, he argues, may be the source of the material's durability.

Many people assume that bees visit whichever flowers offer the most nectar. Ecologist Hiroshi Tanaka observed that bumblebees in his study area often passed over nectar-rich flowers in favor of ones with less nectar that were closer together. Because each flight between flowers costs energy and time, he argues, a patch of modest flowers packed tightly can provide more food per minute than scattered flowers that each contain more.

When the town of Millbrook painted its crosswalks in bright, rainbow stripes, officials expected the change to be purely decorative. Over the next year, however, the number of accidents involving pedestrians at those crossings fell by more than a third. Traffic engineers think drivers simply noticed the colorful crossings sooner and slowed down.

Researchers have long known that sleep helps people remember what they learned during the day. A study led by neuroscientist Daniela Ortiz suggests that timing matters too. Students who studied vocabulary in the evening and slept within three hours remembered more words a week later than students who studied in the morning, even though both groups slept the same total number of hours.

Community gardens are often promoted as a way to grow cheap, fresh food. A survey of gardeners in three cities by public health researcher Lena Fischer found that food was rarely the main reason people joined. Most said they came for the company of neighbors and the chance to spend time outdoors; many grew mainly flowers.

The following text is from a novel. Teodora is waiting for news about a job.

She told herself she was not waiting. She washed the windows, which did not need washing; she alphabetized the spice rack and then, finding the result unsatisfactory, arranged it by color. Each time a car slowed in the street she found she had stopped moving, the cloth in her hand, until the engine sound had passed.

Many cities have tried to reduce litter by adding more public trash cans. A study of four neighborhoods by environmental planner Kwame Mensah found that the number of bins mattered less than their condition. Streets with fewer but regularly emptied, undamaged bins had less litter than streets with many overflowing ones. Overflowing bins, Mensah suggests, signal that nobody is looking after a place, and people litter more where they think nobody cares.

The violin maker Antonio Stradivari is often said to have possessed a secret, perhaps a special varnish, that made his instruments sound uniquely beautiful. In blind listening tests organized by acoustician Clara Beaumont, however, experienced violinists who played both old Italian violins and high-quality modern ones could not reliably tell which was which, and many preferred the modern instruments. Beaumont suggests that the reputation of the old violins rests at least partly on their history and price rather than on their sound alone.

Volcanic islands are usually thought of as hostile to life when they first form: bare rock, no soil, little fresh water. Yet biologist Sigrid Halvorsen found spiders on a new volcanic island off Iceland within months of its eruption, long before any plants had appeared. The spiders, carried by the wind on threads of silk, survived by eating insects that had also blown in. Halvorsen argues that the first food webs on new land may be built not on plants, as is often assumed, but on a steady rain of airborne animals.

The following text is from an essay about maps.

Every map is a set of decisions. To show a road, the mapmaker must decide that roads matter more than, say, the hedges beside them; to fit a country on a page, she must decide which distortions of shape or size are acceptable. A map that seems simply to show the world as it is has only hidden its decisions well.

Economists have traditionally assumed that people value a dollar the same whether they win it, earn it, or find it. Behavioral economist Ruth Ndlovu tested this by giving participants equal sums labeled either as 'bonus' or as 'wages'. Those whose money was labeled a bonus spent it on treats and gifts far more often, while those paid 'wages' tended to save it or use it for bills. Ndlovu concludes that the way money is framed shapes how it is spent, even when the amount is identical.

The following text is from a novel. Mr. Abernethy has just retired after forty years as a stationmaster.

On the first Monday of his retirement Mr. Abernethy rose at five, as he always had, shaved, and put on his good jacket. He was halfway to the door before he remembered. He stood in the hall for some time, listening to the 6:12 pass through the valley without him, and then, because there seemed nothing else to do, he took off the jacket and hung it up very carefully, as if it might be needed again.

It is often said that bilingual children start speaking later than children who learn one language. A review by linguist Samira Benali of studies covering several thousand children found no such delay: bilingual children produced their first words and first sentences at the same ages as monolingual children. What the review did find is that bilingual children's vocabulary in each separate language was sometimes smaller, but their total vocabulary across both languages was similar to that of monolingual children.

In the 1700s, the British navy lost far more sailors to scurvy than to battle. Today it is often said that the cure, citrus fruit, was discovered and then immediately adopted. In fact, the history was messier. Naval surgeon reports show that some captains found citrus effective decades before it became official policy, while others, using juice that had been boiled and stored for months, saw no effect at all and concluded the remedy was useless. The mixed results delayed its adoption for years.

Climate scientists sometimes describe glaciers as the planet's 'water towers', storing winter snow as ice and releasing it as meltwater during dry summers. As glaciers shrink, some rivers fed by them have temporarily carried more water than usual, since the ice is melting faster. Hydrologist Mateus Pinheiro warns that this increase is misleading: once a glacier has shrunk past a certain point, summer flow will fall sharply, leaving communities that had come to rely on the extra water facing shortages.

Scholars of the poet Elisabeth Varga have often read her late poems, which are full of images of empty rooms and closed doors, as expressions of loneliness in her final years. Biographer Tomasz Wierzbicki points out, however, that Varga wrote these poems during the busiest social period of her life, when her house was constantly full of guests. He suggests that the empty rooms may represent not loneliness but a longing for solitude she could no longer find.