Plastic has polluted the countryside and been     1    threat to wildlife for decades. In the last century or so, environmentalists have urged us     2    (cut) the amount of plastic we use or recycle the plastic bags. However, with only less than 14 percent of the total amount recycled, people are still struggling with plastic pollution     3    (global).

There may be a solution. Recently scientists have made a biodegradable (可降解的) plastic,     4     means the billions of plastic bags, cups, straws, etc. that we throw away each day could be recycled.     5     (compare) with ordinary plastics, they could break down as naturally as organic waste. They could do it within a few weeks,     6     (use) just heat and water. The new, biodegradable plastic has polyester-eating enzymes (酶) inside it. When these enzymes are exposed     7     heat and water, they eat away at the plastic and turn it into “food” for the soil. Professor Ting Xu said up to 98 per cent of the plastic her team made reduced into tiny pieces. She said: “The study gives us a     8     (believe) that this continuing problem of single-use plastics can    9    (solve) in the near future.” She added: “Look at all the wasted stuff we throw away—clothing, shoes, electronics....We are taking things from the earth at a     10     (fast) rate than we can return them.”

A terrible earthquake hit the city of Tangshan on July 28, 1976, in which thousands of people died and many     1    (injure). Many houses fell down and sand filled the wells instead of water. People were greatly shocked. All the electricity in the city was cut     2    and people started to wonder how long the disaster would last. The whole city was     3    (complete) destroyed and the world seemed at     4    (it) end.

The people of Tangshan didn’t lose hope, because 150,000 soldiers were sent     5    (help) the rescue workers. The soldiers tried their best to dig out those     6    were trapped. Workers built shelters for the     7    (survive). Fresh water was taken to the city by every means. Slowly, the city started to come back to life.

It was said that before the quake, strange things were happening in     8    countryside. The water in the village wells     9    (rise) and fell. Fish jumped out of the ponds. Strange noises were heard in the sky,    10    people thought little of them.

At 8, 844.43 meters high, Mount Qomolangma is the     1    (tall) mountain on Earth. While it is famous for     2    (it)challenging hike, parts of the mountain are facing a problem: garbage. Every year,   thousands of     3    (visit) throw away tons of trash, including soda cans and plastic bags.

According to the UN, over 140 tons of trash have been left on the mountain. To reduce trash, China is limiting the number of   people     4    can climb the mountain’s north side. Only 300 people will     5    (allow) to climb it each year, and only during spring.

Local residents cleaned the mountain last year,     6    (remove) trash at a height of 5, 200 meters. They     7    (collect) about 8.4 metric tons of trash, according to figures from the Tibet autonomous region' government (西藏自治区人民政府).

This year, the local government plans to spend 4 million yuan     8    a new clean-up campaign, setting up stations to sort, recycle and break down garbage collected from the mountain. In addition to trash, workers will also collect the bodies of     9    (die)climbers. As of the 2019 climbing season, more than 300 people have died on Qomolangma, with 12 deaths this year.

A group of artists will try to turn some trash into artwork. They will show these works    10    (local) to remind people not to leave trash when climbing the mountain.

Before the Tangshan earthquake, strange things happened. A     1    (smell) gas came out of the cracks of wells and animals     2    (become) nervous. At 3:42 am, everything began to shake. It seemed as if the world was at     3     end. In fifteen seconds, a large city lay in     4    (ruin), and the number of people who were seriously     5    (injure) or killed reached more than 400,000. Water, food and     6    (electric) were hard to get and the railway tracks were     7    (use) pieces of steel. But all hope was not lost. The rescue teams that were     8    (organize) by the army came to help those     9    (survivor). Slowly, the city began     10    (breathe) again.

Throughout history, people have thought of the ocean as a diverse and limitless source of food. Yet today there is clear evidence that the ocean has a limit. Most of the big fish in the ocean are now     1     （go）. One major cause is overfishing. People are taking so many fish from the sea that many species cannot replace     2    （they）.

For centuries, local fishermen caught only enough fish for their own and their community’s needs. However, from the early 20th century, people around the world became interested     3     consuming protein-rich foods. People began     4    （catch）large quantities of fish for profit and selling them to worldwide markets. In a very short period of time, commercial fishing     5    （great）reduced the number of large predatory（掠食的）fish, such as the cod and tuna.

Today, there are still plenty of fish in the sea,     6     they’re mostly just the little ones. Small fish,     7     include sardines and anchovies, have more than doubled in number — largely because there are not enough big fish     8    （eat）them.

Such large fish     9    （be）necessary, because they hunt and kill the sick and weak smaller fish. Without weeding out the weak, or survival of the fittest, ecosystems would become less stable. As a result, fish are less able to survive     10    （difficult）such as pollution, environmental change, or changes in the food supply.