SAT Reading and Writing Practice Test: Text Structure and Purpose

Many animals change color slowly, over days or seasons. The common octopus can do it in less than a second. Its skin contains thousands of chromatophores, tiny sacs of pigment surrounded by muscles that the nervous system can stretch or squeeze. When the muscles pull a sac open, the pigment spreads over a wider area and that spot of skin darkens. Because each sac is controlled directly by nerves, the octopus can produce flickering patterns that match a rocky seafloor almost instantly.

For decades, critics treated the novelist's use of regional dialect as a weakness, arguing that it made her characters seem quaint. The novelist herself had trained as a folklorist and spent years recording the speech of farming towns along the river where she grew up. Read with that background in mind, the dialect in her fiction looks less like decoration and more like careful documentation of how real people talked.

City planners in many places have tried to reduce traffic by widening highways. At first, the extra lanes usually do move cars faster. Within a few years, however, traffic often returns to its old level, because faster roads encourage people to drive more often and to live farther from work. Economists call this pattern induced demand. Some planners now argue that adding bus lanes or improving train service is a more lasting way to shorten commutes.

The kitchen clock had stopped at ten past four sometime during the winter, and no one had bothered to fix it. Marta's grandmother liked it that way. "Now it is always time for tea," she said, setting out two cups whenever Marta visited, no matter the hour.

Researchers studying honeybees found that hives placed near fields of flowering clover produced more honey than hives placed near cornfields. The researchers caution, however, that the clover hives were also located in a sheltered valley with lighter winds, so wind conditions, and not only the available flowers, may help explain the difference.

Most maps of the ocean floor are far less detailed than maps of the Moon's surface. One reason is that seawater blocks the radio waves and light that satellites use to measure distances on land. To chart the seafloor in detail, ships must instead send sound pulses downward and time their echoes, a slow process that covers only a narrow strip at a time.

The high-wheel bicycles of the 1870s had pedals attached directly to an enormous front wheel. Because one turn of the pedals meant one turn of the wheel, a bigger wheel carried the rider farther with each stroke. The design had a cost: riders sat so high that a sudden stop could throw them over the handlebars. The chain-driven "safety bicycle," with two wheels of similar size, solved the problem by letting a smaller rear wheel turn several times for each turn of the pedals.

Archaeologists long assumed that the small clay tokens found at many ancient village sites were game pieces. A team studying one site noticed that the tokens come in only a few shapes and are usually found in storerooms beside jars that once held grain. The team proposes that the tokens were used to keep count of stored goods.

The train pulled away, and Daniel waved until it disappeared around the bend. Only then did he notice that he was still holding his sister's umbrella. He looked up at the gray sky and laughed.

Some people think public libraries are becoming unnecessary now that so much information is online. But libraries do more than lend books. Many offer free internet access to people who have none at home, help job seekers prepare résumés and host classes for adults learning English. For many communities, closing a library would mean losing these services, not just a collection of books.