Sea otters live along the Pacific coast. An otter often puts a rock on its chest and hits a shellfish against it to crack the shell. What does the passage say the otter uses to crack shellfish?

The Liberty Bell hangs in Philadelphia. It cracked after years of use, so workers stopped ringing it, but visitors still come to see it today. What can you conclude about how people view the bell now?

Most of Earth's fresh water is hard for people to use. Much is frozen in glaciers or lies underground. People build reservoirs to store water for homes, farms, and businesses. What does the passage say about most of Earth's fresh water?

A bicycle brake helps a rider slow down. Squeezing the brake lever presses pads against the wheel rim. Friction between the pads and the turning wheel slows the bike. What creates the friction that slows the wheel?

The Sahara is the world's largest hot desert. It has sand dunes, rocky plains, mountains, and dry valleys. Some oases have water near the surface. What can you conclude about crossing the Sahara?

Bees help flowering plants make seeds. As a bee gathers nectar, pollen sticks to its body. When it visits another flower, some pollen rubs off and helps the plant grow seeds. What happens as a bee gathers nectar?

The Erie Canal opened in 1825, connecting the Hudson River with Lake Erie. Before it, moving goods between the Great Lakes and the Atlantic coast was slow and costly. What does the passage say the canal did for trade?

A thermometer measures temperature. In a liquid thermometer, the liquid expands and rises in a glass tube when warmed, and contracts and falls when it cools. Why does the liquid move up and down in the tube?

Mount Rushmore is carved into granite in South Dakota. It shows the faces of Washington, Jefferson, Roosevelt, and Lincoln. Work began in 1927 and ended in 1941. How many presidents' faces does the sculpture show?

A solar eclipse happens when the Moon moves between Earth and the Sun. The Moon's shadow falls on only part of Earth. People in the darkest part may see the Sun fully covered. What does the passage say about who sees the darkest shadow?

Paper recycling starts when used paper is collected and sorted. Workers remove plastic or metal, then mix the paper with water to make pulp, and screens remove small bits of glue. What can you conclude about recycling paper?

The Mississippi River begins in Minnesota and flows south to the Gulf of Mexico. Smaller rivers flow into it, and barges carry loads of grain and fuel along it. What can you conclude about the Mississippi River?

The Pony Express carried mail across the West from 1860 to 1861. Riders changed horses at stations to keep mail moving. It ended after the telegraph began sending messages faster and for less money. Why did the service end?

A volcano is an opening in Earth's crust where melted rock reaches the surface. Melted rock underground is called magma. After it erupts, it is called lava. What is the difference between magma and lava?

The Great Wall of China is not one single wall. Different rulers ordered walls and watchtowers built over many centuries, using materials found nearby such as earth, brick, or stone. Who ordered the Great Wall to be built?

A camera focuses light to make a picture. Light enters through the lens, which bends it to form a sharp image on a sensor or film. If the lens is not adjusted correctly, the image looks blurry. What must happen for a clear image?

Mangrove trees grow in salty coastal areas in warm parts of the world. Their roots often rise above the muddy ground and water. These roots help the tree get oxygen in soggy soil. Why do mangrove roots rise above the ground?

The Wright brothers tested gliders and studied how wings could lift a machine before their Flyer made the first powered flight at Kitty Hawk in 1903. What can you conclude about how they built the Flyer?

Compost forms when plant scraps break down. Tiny organisms such as bacteria and fungi help decompose the material, and worms and insects break pieces into smaller parts. Which tiny organisms does the passage say help decompose compost?

The Grand Canyon was carved mainly by the Colorado River over a long time. Wind, rain, freezing, and thawing also helped widen the canyon. What can you conclude about how the canyon was shaped?