City engineers recently studied how water moves through the downtown distribution system. In the early morning, when many people turn on taps at once, pressure drops in several neighborhoods. The data showed that dozens of neighborhood pipes all feed into a single, older tunnel beneath the river. Because that tunnel is much narrower than the pipes that lead into it, it becomes a choke point for the system. Water approaches quickly, but the narrow passage slows the flow, like the neck of a bottle. Upstream, pressure builds and meters spike; downstream, faucets can sputter as the flow thins out. To fix the problem, the engineers propose adding a parallel tunnel so water has another path around the choke point. They would also install sensors on both sides of the river to confirm that pressure stays steady during the morning rush. With the restriction eased, they expect a smoother flow and fewer complaints from households who have gotten used to weak showers at the busiest times.

What does the phrase choke point most nearly mean as used in the passage?

For months, the state has measured less rain than usual. On the prairie, grasses crisp underfoot, and the river that once surged past the town bridge now creeps along. In late summer, its flow dwindled to a thread winding between sun-baked stones. That thin line still moves, but it leaves wide shoulders of exposed riverbed where mussel shells lie like dropped cups. Farmers watch the gauges and schedule irrigation sparingly; every gallon they draw from the aquifer is like taking money from a savings account. Withdraw too much, and the balance falls. Conservation crews plant native shrubs whose deep roots hold soil and sip less water. When a brief storm finally arrives, the thirsty ground drinks the first drops so quickly that little runs off to refill the stream. Officials call for smart water habits—short showers, leak fixes, and turning off hoses—so the thread of flow can survive until the wetter season returns.

What does the word "thread" most nearly mean as used in the passage?

When the principal announced that school would start five minutes earlier next month, it sounded like a tiny change. But that small shift created a ripple effect across the schedule. Bus routes had to be tightened so students would still arrive on time. Breakfast service moved up so there would be enough time to eat. Crossing guards adjusted their shifts to match the new bell. In the library, the morning checkout cart needed to be ready sooner, and the student volunteers swapped duties to make it work. Even after-school tutoring ended five minutes earlier to keep the buses on the same timetable. Like a pebble dropped into a pond, one small circle spread into the next, touching almost every routine in the building. The early bell did not just affect the first class; it set off a series of related changes that reached many people and places.

What does the phrase ripple effect most nearly mean as used in the passage?

In regions that were once logged or grazed, wildlife managers sometimes reintroduce beavers. Unlike predators, these animals remodel water. Using branches and mud, they build dams that slow a rushing stream, spreading it into a chain of ponds. As the water lingers, sediment settles, raising the water table and soaking nearby soils. Willow and cottonwood seedlings take hold in this wet ground. Their shade cools the ponds, which helps insects and young fish survive summer heat. The new pools also give ducks and herons places to feed. Biologists describe these connected changes as a cascade: one action sets off many others, each enabling the next. The term doesn't refer to a scenic waterfall here. It points to a sequence of effects that grow from a single cause. Because beaver dams store water, they can keep a valley greener during drought and slow floods after big storms. In this way, a few gnawed sticks can rewrite the map of a creek and the lives that depend on it.

What does the word "cascade" most nearly mean as used in the passage?

Scientists who study honeybees often watch the "waggle dance," a figure-eight shuffle bees use to share directions to food. The angle of the bee's waggle lines up with the sun, and the length of the waggle tells other bees how far to fly. To test whether the message was understood, researchers set sugar-water feeders at different distances from the hive. But first they had to calibrate their setup. They measured the space between the hive and each feeder and adjusted the positions until the distances matched the times and angles they expected from the dance. Without careful calibration, a feeder might be too close or too far, and the bees' responses would be hard to interpret. They repeated this check each morning because the sun's position shifts, which nudges the dance by a few degrees. By matching their equipment to these small changes, they avoided misleading results and could decode the dance more confidently: a longer waggle meant a farther feeder, and a slight shift in angle meant a turn toward a new patch of flowers.

What does the word "calibrate" most nearly mean as used in the passage?

Sound moves through a forest in surprising ways. A thick canopy and layers of leaves act like blankets, softening sharp noises before they travel far. Pine needles and mossy ground absorb echoes, so footsteps seem to fade quickly. In contrast, a bare, rocky slope can bounce sound back, making a shout seem louder and clearer. Animal calls are shaped by these conditions. Woodpeckers drum on hollow trunks because the vibrations carry better than a whistle through dense foliage. During rain, the hiss of falling drops can mask quiet sounds, so birds switch to simpler, stronger notes. In this setting, the same leafy layers that shelter the understory also muffle footsteps and speech, turning them into gentler, hushed versions of themselves. Park designers plant rows of trees along busy roads for a similar reason: the greenery does not stop traffic, but it reduces the harshness of engine noise for nearby homes.

What does the word muffle most nearly mean as used in the passage?

Weather satellites orbit high above Earth, scanning clouds, land, and oceans with sensitive detectors. Each detector converts light or heat into a number, which computers turn into the colorful images people see on the news. But numbers can drift over time as parts age or as the spacecraft moves from hot sunlight into cold shadow. To keep the data trustworthy, engineers routinely calibrate the sensors. They point the instruments at known sources, such as deep space, which should read near zero, or onboard targets that have a carefully controlled temperature. Then they adjust the instrument settings until the readings match what is expected. Ground stations also help by launching weather balloons and comparing those measurements with the satellite's view of the same air. When the values line up, forecasters can be confident that a bright patch on the image truly means thick clouds, not a sensor error. Regular calibration doesn't change the weather, but it makes our picture of it clear.

What does the word "calibrate" most nearly mean as used in the passage?

On hot summer days, cities can feel several degrees warmer than nearby suburbs. This pattern is called the urban heat island. It doesn't float on water; instead, it stands apart because its temperatures rise above those around it. One reason is surface albedo—a measure of how much sunlight a surface sends back into the sky. Light-colored roofs and bright sidewalks have high albedo, bouncing away much of the sun's energy. Dark asphalt and tar have low albedo, so they soak up sunshine like a sponge and store heat through the afternoon. Trees also play a role. Their leaves release moisture into the air, a process that cools neighborhoods the way sweat cools skin. Where trees are sparse and pavement stretches in wide sheets, the air can stagnate. As evening arrives, that stored warmth leaks back into the streets and alleys. In this long, gentle exhale, the city seems to breathe: its temperature rises during the day and slowly falls at night. Simple changes can help. Painting roofs a lighter color raises albedo. Planting rows of street trees casts shade and stirs breezes. Even small patches of garden can break up hard surfaces so they don't drink in so much heat.

What does the phrase "soak up sunshine like a sponge" most nearly mean as used in the passage?

On hot summer days, cities can feel several degrees warmer than nearby suburbs. This pattern is called the urban heat island. It doesn't float on water; instead, it stands apart because its temperatures rise above those around it. One reason is surface albedo—a measure of how much sunlight a surface sends back into the sky. Light-colored roofs and bright sidewalks have high albedo, bouncing away much of the sun's energy. Dark asphalt and tar have low albedo, so they soak up sunshine like a sponge and store heat through the afternoon. Trees also play a role. Their leaves release moisture into the air, a process that cools neighborhoods the way sweat cools skin. Where trees are sparse and pavement stretches in wide sheets, the air can stagnate. As evening arrives, that stored warmth leaks back into the streets and alleys. In this long, gentle exhale, the city seems to breathe: its temperature rises during the day and slowly falls at night. Simple changes can help. Painting roofs a lighter color raises albedo. Planting rows of street trees casts shade and stirs breezes. Even small patches of garden can break up hard surfaces so they don't drink in so much heat.

What is the impact of the word "island" in the term "urban heat island"?

Glaciers are rivers of ice that creep downhill under their own weight. Although they move only inches or feet in a day, their patience gives them power. As a glacier slides, it drags rocks along its base like sandpaper. It also freezes around boulders and plucks them free. Over years, these actions gnaw at the landscape, carving U-shaped valleys and leaving behind polished rock. Meltwater seeps into cracks, refreezes, and wedges the rock apart, adding to the slow work. To people, the change can be hard to notice from one season to the next. Yet when scientists compare old photographs with new ones, the results are clear: where a sharp ridge once stood, a gentler curve remains. The word gnaw is useful here because it suggests a steady, persistent kind of wearing down, not a single dramatic bite. No cliff collapses in one moment; instead, tiny pieces are removed again and again until the whole surface is reshaped.

What is the impact of the word gnaw on the meaning of the passage?