The Yellow River is the second longest river in China and the sixth longest in the world at the estimated
The Yellow River
2 . Coral reefs are some of the most diverse and valuable ecosystems on Earth. Coral reefs support more species per unit area than any other marine (海洋的) environment, including about 4,000 species of fish, 800 species of hard corals and hundreds of other species. Scientists estimate that there may be millions of undiscovered species living in and around reefs. This biodiversity is considered the key to finding new medicines for the 21st century. Many drugs are now being developed from coral reef animals and plants as possible cures for cancer, viruses, and other diseases.
Healthy coral reefs support fisheries as well as jobs and businesses through tourism and recreation. About half of all managed fisheries depend on coral reefs and related habitats for a part of their life cycles. The National Marine Fisheries Service estimates the commercial value of U. S. fisheries from coral reefs is over $ 100 million, Local economies receive billions of dollars from visitors to reefs through diving tours, recreational fishing trips, hotels, restaurants, and other businesses based near reef ecosystems.
Coral reef structures also buffer (缓冲) shorelines against 97 percent of the energy from waves, storms, and floods, helping to prevent loss of life, and property damage. When reefs are damaged or destroyed, the absence of this natural barrier can increase the damage to coastal communities from normal wave action and violent storms. Several million people live in U. S. coastal areas near coral reefs. Some coastal development is required to provide necessary infrastructure (基础设施) for coastal residents and the growing coastal tourism industry.
Despite their great economic and recreational value, coral reefs are severely threatened by pollution, disease, and habitat destruction. Once coral reefs are damaged, they are less able to support the many creatures that live on them and the communities near them. When a coral reef supports fewer fish, plants, and animals, it also loses value as a tourist destination.
1. Why is biodiversity important to medicines?| A．It can reduce the prices of new medicines. | B．It can help make new medicines. |
| C．It can be used for medicines. | D．It can be used to cure diseases. |
| A．They protect people against sharks. | B．They completely avoid serious flooding. |
| C．They prevent people from being drowned. | D．They weaken most of the energy from waves. |
| A．Most fish will die out. | B．Coastal cities will attract fewer tourists. |
| C．There will be no large fish. | D．The sea will be polluted. |
| A．The Importance of Diverse Ecosystems | B．The Environments of Coral Reefs |
| C．The Importance of Coral Reefs | D．The Value of Biodiversity |
