A guide explains: "Sound travels as each air particle bumps the next, like a nudge running down a line of dominoes. But the air reforms instantly, while fallen dominoes stay down." How does the first sentence connect sound to dominoes?

An article states: "Both glaciers and rivers carve valleys. Ice grinds a broad U-shaped trough; water cuts a narrow V. Rivers move in hours what ice shifts in decades." What distinction does the article draw?

A textbook writes: "White blood cells act like border inspectors, checking each arrival for the right markers. Unlike inspectors, the cells keep no written record." What does the comparison help readers understand?

A report explains that runny lava spreads into wide, low shields, while thicker lava, piling near the vent like cooling honey, builds steep cones. How does the report organize its information?

A profile reports: "Alvarez and Boone each built early sorting machines. Alvarez wanted faster mail; Boone wanted a machine that never tired. They never met or exchanged plans." What distinction does the profile draw?

A manual explains: "A battery stores charge as a bucket stores water. A bigger bucket holds more; a wider spout empties it faster. Unlike a bucket, a battery cannot be checked by looking inside." What does the comparison clarify?

A field guide divides shore birds into three groups. Waders stalk prey on foot, divers plunge beneath the surface for fish, and skimmers slice the water with their lower bills. What principle organizes the guide's groups?

An article notes that a new stadium roof spans 900 feet, about the length of three 300-foot football fields placed end to end. Why does the writer mention football fields?

A report links two events: a drought thinned the hillside grass, and a flood months later stripped the soil away, since fewer roots remained to hold the ground. What connection does the report draw?

A writer says: "A coral reef is an apartment building for the sea, housing many species in one structure. But no landlord built it. Its own tenants did, and it is still alive." What distinction does the writer draw?

A report first sorts bridges into three kinds, then explains that a suspension bridge hangs its deck from cables the way a hammock hangs between two trees. Which technique explains how the deck is held?

An editorial separates weather from climate and adds that one cold week does not undo a warming climate. What distinction between the two ideas does this point rely on?

A profile sets two mayors side by side: Ruiz raised the money before starting each project; Delgado started first and raised money afterward. Each finished the same number of parks. What comparison does the profile make?

A science writer says an atom resembles a solar system, with electrons circling a nucleus, then warns that the picture misleads because electrons occupy fuzzy regions, not fixed paths. Why include the warning?

A museum places a Roman chisel beside a modern box cutter, and a colonial ruler beside a laser tape measure. What does this arrangement emphasize about the tools?

To explain the city budget, a council compares its yearly income to a household paycheck and its long-term debt to a thirty-year mortgage. What does the comparison help residents understand?

A history article says: "The canal and the railroad both carried grain east. The canal froze each winter, but the trains ran all year." What relationship does the second sentence draw?

An article explains that certain gases hold heat near the ground the way a blanket holds in body heat. What does the comparison clarify about the gases?

A report pairs two walkouts at one mill: the spring strike won shorter hours, the fall strike won nothing, and both drew the same number of workers. What point does pairing them make?

A report splits energy sources into renewable and nonrenewable and places natural gas with coal, even though gas burns more cleanly. On what basis is gas most likely grouped with coal?