There are many famous cities in the world.

The Honghe Hani Rice Terraces(梯田), in southern Yunnan, China, cover a huge 16, 603-hectare area. The terraces,     1    (know)to all of the world now, were made out of a thick forest by the Hani people. The terraces rise at different angles from a shallow 15°    2     a steep 75°, forming a wonderful landscape(景观)that     3    (be)rare in the world.

In 2003, the terraced fields were     4    (official)recognized by UNESCO as a World Cultural and Natural Heritage site. About 1,300 years ago, the Hani people first     5    (come)to the steep mountains. They struggled against the difficult terrain(地形), successfully creating the terraces, where they grew rice in order to make     6    (they) living. Over the past 1,300 years, the Hani people have developed a complex system of channels     7    (bring)water from the forested mountaintops. They show great appreciation for natural phenomena such as rivers, mountains, the sun, fire     8     the moon. They have also created a complete farming system     9     involves cattle, ducks, and fish and supports the     10    (produce)of red rice, the area's main crop.

The landscape changes through the year. In April the terraces are all green as rice starts to grow; in later parts of the year it is yellowish brown as the rice ripens. In February, the terraces become bare earth, with the water reflecting(反射)the sky.

3 . 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.

The Xi’an City Wall is the most complete city wall that has survived China’s long history. It     1     (build) originally to protect the city     2     the Tang dynasty and has now been completely restored (修复). It is possible       3     (walk) or bike the entire 14 kilometers.

We accessed the wall through the South Gate. The wall is 12 meters high and from here you can see streams of people moving inside and outside the City Wall.

After     4     (spend) some time looking at all the defensive equipment at the wall, we decided it was time for some action and what     5     (good) than to ride on a piece of history!

We     6     (hire) our bikes from the rental place at the South Gate. My bike was old and shaky     7     did the job. It took us about 3 hours to go all     8     way around the Xi’an City Wall. Supposedly you can do it in two hours, but we stopped at the different gates and     9     (watchtower) to take pictures or just to watch the local people going about their     10     (day) routines.

The highest point on Earth has a     1    (new) announced height. Mount Everest is 29,031. 69 feet above sea level, according to survey results presented today. That is more than two feet higher     2    the altitude previously recognized by the government of Nepal.

The height,     3     was announced on December 8 in a joint     4    (state) by the Survey Department of Nepal and Chinese authorities, is the result of a multiyear project to measure the mountain. As the first serious survey of Everest in 16 years, the effort has been closely followed by the geographic community—particularly scientists analyzing how a devastating 7. 8 magnitude earthquake in 2015     5    (affect) the region.

Last spring a small group of Nepalese surveyors and guides experienced the     6    （bite) wind of a nighttime climbing, reaching the top at 3 a. m. local time.

“We long     7    (deliver) the message that we can do something with our own resources and     8    (technique) manpower,” Khimlal Gautam, chief survey officer for the project, told National Geographic last year.

In 1856, mathematician Radhanath Sickdhar found that Everest was the     9     (high) mountain in the world while he was working for the Great Trigonometrical Survey, a project devoted to surveying and mapping the Indian subcontinent. Since then, a handful     10     surveys have sought to pin down the mountain's true height with the best technology available at the time.

China's national observatory on Monday issued a yellow alert for sandstorms in the northern part of the country. “    1    （start）from Monday to 8 a. m. Tuesday, affected by cold fronts and heavy winds, floating sand and dust       2    （expect）to sweep parts of several northern provinces and the city of Beijing,”     3    （forecast）the NMC.

Some regions in Inner Mongolia, Ningxia, Shaanxi and Shanxi were hit by strong sandstorms. The capital Beijing was enveloped in yellow dust     4     Monday morning with visibility at less than 1 km,     5     followed an official yellow warning for the sandstorm. The sandstorm is the strongest and the most sweeping     6     in nearly a decade. Remote sensing images of dust in northern China show the dust from Mongolia     7    （gradual）traveled south with the airflow.

This wave of sandstorms is a result of the combined       8    （effect）of cold air and cyclones from Mongolia. “The combined action of the Mongolian cyclone and the cold high     9    （press）provided a strong impetus（动力）for the sandstorm,” said Zhang Bihui,     10     senior engineer with the NMC.