The world itself is becoming much smaller by using modern traffic and modern communication means. Life today is much easier than it was hundreds     1    years ago, but it has brought new problems. One of the     2    (big) is pollution. Pollution comes in many     3     (form). We see it, smell it, drink it and even hear it.

Man has been polluting the earth. The more people, the more pollution. Many years ago, the problem was not so serious     4     there were not so many people. When the land was used up or the river was dirty in one place, man     5     (move)to another place. Man is now     6     (slow) polluting the whole world.

Air pollution is still the most serious.Water pollution kills our fish and pollutes our drinking water. Noise pollution     7     (make) us angry more easily.

Many countries are making rules     8     (fight) pollution. They stop people from burning coal in houses and the factories in the city, and from     9     (put) dirty smoke into the air.

The earth is our home. We must take care of     10    . That means keeping the land, water and air clean.

Arctic foxes live on the land and sea ice within the Arctic Circle. Winter in the Arctic is unlike winter in most parts of the world. From October to February, the sun never rises to give    1     (warm)and light.

    2     (luck), these small foxes have     3     (use)adaptation for living in the icy Arctic.Their thick fur coat keeps their body at a comfortable 104°F. Their long tails act like a blanket,     4     (keep)the Arctic foxes warm when they wrap the tails around their body to sleep. And their white coats make it difficult for predators(掠食动物) such as wolves and polar bears to find     5     (they) among the ice and snow.

When they don’t need     6     (avoid) predators or keep warm, Arctic foxes are    7     the hunt for food. They prefer to eat small rodents(啮齿动物), but when times are tough they 'll eat    8     they can find.

If an Arctic fox can't find food, or if the weather    9     (get) really bad, it can dig a snow hole and hunker down(蹲下) for up to two weeks. Once the animal can get out of its hole, it'll try to hunt again. With food in its belly, the Arctic fox has     10     better chance of making it through another long, dark winter.

With the rapid extinction of many wild species, more and more people come to realize the great importance of wildlife protection.

We have to understand the problem in     1     new light: we protect ourselves through protecting wildlife. On the one hand, any species of wildlife helps to keep the ecological balance(生态平衡).     2     one species becomes extinct, it will disappear forever. What is more, it will result     3     the extinction of a chain of wildlife, which may lead to unpredictable disasters. On the other hand, the modern science and technology makes     4    possible for us to learn more about wildlife. By now, scientists     5    (find) that wildlife has unknown genetic codes(遗传密码), which may turn out     6     (free) human beings from serious diseases and     7     (nature) disasters in the future.

It is necessary for us to protect wildlife     8    (immediate) before it is too late, although man has already polluted the environment and threatened the     9    (exist) of many wild species. Let’s take action to protect wildlife.     10    (learn) to live in harmony with all wildlife is part of modern civilization.

The first Smokey Bear poster shows a brown-coated bear wearing jeans. He is staring     1     （shy） up from under a campaign hat as he pours a bucket of water over a campfire. “SMOKEY SAYS,” the poster     2    （read） , “Care will prevent 9 out of 10 forest fires!”

Albert Staehle, the illustrator, chose a bear because he might have wanted Smokey     3     （look） like the father of the forest, as his wife supposed. But many will forever associate the cartoon with a real baby bear,     4     paws（爪子）were burnt in a 1950 spring wildfire.

The baby bear had been rescued by Ray Bell, a forest ranger （护林员）     5    （ fight） a fire in New Mexico's Capitan Mountains. Don Bell was 15 when his father came home with the five-pound bear. The Bell family was constantly taking in wild animals to protect them     6     potential dangers, so Don Bell didn't think much of the "cute little guy" who slept in a rabbit cage. But the story of the rescued baby bear would become     7     national phenomenon. At the capital airport, the     8     （arrive） of Smokey drew hundreds of reporters, photographers and onlookers, and he appeared in     9    （newspaper） across the country.

At the zoo, Smokey drew millions of visitors during 26 years. Having a living animal symbol helped make the wildfire-safety campaign more visible. The Smokey ads were also a far     10    （ good） choice.

Up to June 23rd , 2020, 55 BeiDou satellites     1     (send) up，meaning the completion of China's self-developed BeiDou Navigation(导航) Satellite System (BDS). BDS appears later     2     America's GPS, Russia's GLONASS and EU's Galileo, but it can match them. As one of the fourth     3     (globe) navigation satellite systems, BDS involves efforts of over 400 agencies and 300,000 research personnel and technicians.

Originally     4     (plan) in the 1980s, the network represents a milestone in China's space effort. BDS is comparable to GPS in terms of the     5     (accurate) of positioning. It also offers short message communication and thus can provide emergency communications in areas     6     conventional communication signals are poor.     7     an effort to improve the quality of their positioning services, Apple and Samsung phones, among others, are already using BDS's signals, and so     8     (be) every Chinese brand.

The construction of complete BDS is a huge technical achievement for China and can     9     (easy) pay off in the near future. Meanwhile, BDS's great contribution to     10     (promote) the world's economic and social development as well as the peaceful use of space has attracted the world's attention.

Twelve laureates were awarded a Nobel Prize in 2020. Their achievements are     1     （benefit）to humankind.

Three scientists, Roger Penrose, Reinhard Genzel and Andrea Ghez,     2     helped uncover the details about black holes, shared this year's Nobel Prize in Physics.

Black holes are massive objects whose gravitational field is so strong     3     nothing can escape it, not even light. At their centers, the laws of physics stop making sense.

No question, these objects are mysterious. Fortunately, the full picture gets clearer than before with scientists     4    （ continuous） working on them. Penrose eventually performed mathematical     5    （ calculation） that showed black holes were not just mathematical ideas     6    （ suggest） by

Einstein^’s theory but that they could form in conditions which are likely to exist in the universe. Using the world’s largest telescopes, Genzel and Ghez each lead astronomers who , since the early 1990s,    7    （focus） on a region called Sagittarius A * （人马座 A 星）at the centre of our galaxy. They     8           （ develop） methods to see through the huge clouds of interstellar （星云）gas and dust     9     the centre of the Milky Way. They also improved new techniques,    10    （ devote） themselves to long-term research. Their pioneering work has given us the most convincing evidence of a supermassive black hole at the centre of the Milky Way.

Many people know that marine mammals，like whales and dolphins，breathe air as we do.    1    , many people don't know that they have developed some interesting sleeping     2     (habit) to adjust to their regular trips up to the surface for air.

    3     ( like ) our own breathing，which does not require any effort，marine mammals must consciously go to the surface of the water    4     ( breathe) through a blowhole on top of their heads. Because of this，they don't sleep for    5     solid 8 hours a night like we do.

Some marine mammals sleep while    6     (swim ). Whales nap for brief periods，during    7    an alert(警觉的）friend guides them. In fact, a young whale must sleep alongside its mother because the mother's slipstream actually pulls the calf along.

Others，like dolphins，sleep while floating on the surface of the water or take short catnaps while floating below the surface.Researchers claim that when they sleep，their brain is always    8    ( partial) alert.Aside from these brief naps，dolphins are active most of the night.

Of course，marine mammals    9    ( equip) to handle underwater sleeping. They have    10    ( large)lungs，exchange air more fully at each breath， and carry more oxygen in their blood than we do, so they can hold their breath long enough to sleep with the fishes.

Huanglong is a beautiful natural area in the northwest part of Sichuan, China. It     1     (locate) in the southern part of the Minshan mountain range, 370 kilometers from the capital, Chengdu. The Huanglong Valley is a special     2    ( attract) here.

Huanglong     3     (get) its name from the river looking like a huge golden dragon in ancient times. It's actually a chain of     4     (pool) that flow through the valley. It runs 2. 5 kilometers to the north. In Huanglong, the soft mineral,     5     is colorless or white, formed a type of rock over thousands of years. This mineral gives the water its     6    ( variety) shades of green, blue, brown_? and     7    ( main) yellow. The waterway with its jewel-colored pools flows between peaks covered with snow like a great yellow dragon     8     (wander) through the mountains. There are about 3,400 of these natural pools throughout the valley .

All, however, are only for viewing. In order to protect the landscape, visitors are not encouraged     9     (go) into the water. As Huanglong is also home     10     several endangered animals, including the panda and the Sichuan golden monkey, hunting and hiking are forbidden here.

Cities usually have good reason for being where they are,     1     a nearby port or river. People settle in these places because they are easy to get to and naturally suited to communications and trade. New York City, for example, is near a large harbor at the mounth of the Hudson River. Over 300 years     2     (it) population grew gradually from 800 people to 8 million. But not all cities develop     3     (slow) over a long period of time. Boom towns grow from nothing almost overnight. In 1896, Dawson, Canada, was unmapped wilderness (荒野). But gold     4     (discover) there in 1897, and two years later, it was one of the largest cities in the West, with a population of 30,000.

Dawson did not have any of the natural conveniences of cities like London or Paris. People went there for gold. They travelled over snow-covered mountains and sailed hundreds of miles up icy rivers. The path to Dawson was covered with thirty feet of wet snow     5     could fall without warning. An avalanche (雪崩) once closed the path,     6     (cause) 63 deaths. For many who made it to Dawson,     7    , the rewards were worth the difficult trip. Of the first 20,000 people who dug for gold, 4,000 got rich. About 100 of these stayed rich men for the rest of their lives.

But no matter how rich they were, Dawson was never comfortable. Necessities like food and wood were very expensive. But soon, the gold that Dawson depended on had all been found. The city was crowded with     8     (disappoint) people with no interest in settling down, and when they heard there were new gold discoveries in Alaska, they left Dawson city as quickly as they     9     (come). Today people still come and go—to see where the Canadian gold rush happened.     10     (tour) is now the chief industry of Dawson City—its present population is 762.