Determine Main Ideas and Summarize Practice Test

Read the passage, then answer the question.

Coral reefs may look like colorful rocks, but they are living communities built by tiny animals called coral polyps. One main idea is that reefs support many ocean species. Polyps build hard skeletons that stack up over time, forming reefs with caves and cracks. Fish, crabs, and sea stars use these spaces to hide from predators and to find food. Although reefs cover less than 1% of the ocean floor, scientists estimate they support about a quarter of all marine species.

Another main idea is that coral reefs protect coastlines. When waves reach a reef, the rough surface breaks up the wave energy. This can reduce beach erosion and help protect buildings during storms. Some islands depend on reefs as a natural barrier because they have few other defenses against strong waves.

However, reefs face serious threats. Warmer ocean water can cause coral bleaching, when corals lose the algae that give them color and energy. Pollution and muddy runoff can block sunlight and make it harder for corals to grow. Overfishing can also harm reefs by removing fish that keep algae from taking over. People are working on solutions, such as creating marine protected areas and reducing pollution from land.

Which statement best describes the two main ideas of this passage?

Read the passage, then answer the question.

Plastic pollution is a growing environmental issue in oceans, rivers, and even on land. One main idea is that plastic enters the environment in many ways. Some trash blows out of bins or falls from trucks. Storm drains can carry litter into waterways after heavy rain. Fishing gear, such as nets and lines, may also be lost at sea. Because many plastics do not break down quickly, they can remain in the environment for decades.

Another main idea is that plastic harms wildlife and ecosystems. Animals may mistake plastic pieces for food and become sick or starve. Birds and sea turtles can get tangled in rings, ropes, or nets, making it hard to swim or fly. As plastic breaks into tiny pieces called microplastics, it can mix into sand and water. Scientists have found microplastics in the stomachs of fish, which can affect the food chain.

A third main idea is that people can reduce plastic pollution with solutions at home and in communities. Using reusable bottles and bags lowers the amount of plastic thrown away. Some cities improve recycling programs and add trash traps to storm drains. Companies are also testing new packaging made from materials that break down more easily. Cleanups along beaches and rivers help, but preventing plastic waste in the first place makes the biggest difference.

Which information is essential to understanding the main idea that plastic harms wildlife and ecosystems?