It is perhaps the most ironic symbol of the life on our planet. The Amazon is the world’s largest and most bio-diverse tropical rainforest and a huge trap for carbon dioxide. The harms of _________ in this vital resource are old news. But now, the time on the clock is running out. It seems that the world’s biggest rainforest is about to turn into the world’s biggest environmental _________. “We are about to collapse,” says Luciana Gati at Brazil’s National Institute for Space Research. “We are in a(n) _________, we need action now.”

Gati has spent years _________ the Amazon from the air. She believes we are as little as five years from a point of no return, where rainforest begins to turn into dry land. It is also the point at which billions of tons of carbon would be _________ into the atmosphere. “It’s a nightmare,” she says.

That nightmare situation is the well-known Amazon _________ point, where the ecosystem can no longer cope with the damage of the forest cutting. Like a domino game, one brick falling will _________ the whole tower to collapse in a heap.

Warnings that this is approaching have now taken on extreme urgency. The rate of deforestation has increased sharply and is fast approaching the theoretical _________. In September, a group of more than 200 experts, including Gatti, released an assessment of the situation. The conclusion: we are on the _________ of disaster.

Scientists first began to seriously worry about a potential Amazon tipping point in about 2000, when some studies warned that a combination of climate change and deforestation could cause the rainforest to __________.

A few years later, a team of Brazilian scientists put numbers on it. They __________ that in central, southern and eastern parts of the Amazon, a loss of 40% of the forest cover from pre-industrial levels, or 3°C warming would reduce rainfall so much that the rest of the forest would die of __________ and turn into a dry land in less than a decade.

The scientists have since __________ that prediction, partly due to the global warming that has happened since 2000. The Amazon is already 1.2°C warmer than it was in pre-industrial times and is warming three times faster than the global __________. At that rate of warming, between 20 and 25% deforestation would be enough to dry up the land and destroy the Amazon completely.

“Either way, we would be wise not to exceed 20%”, says a scientist, “for the commonsense reason that there is no point in __________   the precise point of limit by tipping it.”

2 . At first, the grains of rice that Ingo Potrykus held in his fingers did not seem at all _________, but inside, these grains were not white, as ordinary rice is, but a very pale yellow — thanks to beta-carotene (胡萝卜素), a building block for vitamin A.

For more than a decade Potrykus had _________ creating a golden rice that could improve the lives of millions of the poorest people in the world, strengthening their eyesight and their _________ disease.

_________ imagining golden rice was one thing and creating one quite another. Year after year, Potrykus and his colleagues ran into one _________ after another until success finally came in the spring of 1999.

At that point, he tackled an even greater challenge. The golden grains _________ pieces of DNA borrowed from bacteria and flowers. It was what some would call Frankenfood, a product of genetic engineering. As such, it _________ a web of hopes and fears.

The debate began the moment genetically engineered crops (GM crops) were first sold in the 1990s, and it has _________ ever since. First to start major protests against biotechnology were European environmentalists and consumer-advocacy groups. They were soon followed by their U.S. counterparts (相对应的人事物).

The hostility is _________. Most of the GM crops __________ so far have been developed to produce a plant that is not harmed by chemicals used to kill weeds (杂草) in the fields. These genetically engineered crops are often sold by the same large, multinational corporations that __________ the weed-killing chemicals that farmers spray on their fields. Consumers have become suspicious (怀疑的).

The benefits did seem small __________ golden rice was developed. It is the first strong example of a GM crop that may __________ not just the farmers who grow it but also the consumers who eat it. In this case, those include at least a million children who die every year because they are weakened by vitamin-A deficiency (缺乏) and an additional 350,000 who go blind.

Many people __________ poverty and hunger look at golden rice and see it as evidence that GM crops can be made to serve the greater public good. They see a critical role for GM crops in feeding the world’s ever-increasing population. As former U.S. President Jimmy Carter put it, “Responsible biotechnology is not the enemy; __________ is.”

3 . To prevent tsunami-caused disasters, several countries worked together to expand the use of a tsunami-detecting system that had been developed in the United States by the National Oceanic and Atmospheric Administration (NOAA). The system________ of an instrument installed on the seafloor — called a tsunameter — that measures pressure changes caused by a passing tsunami. The tsunameter sends a signal to a surface buoy (浮标), which sends the data to a satellite, which ________ the information to warning centers around the world.

By 2004 only six such detectors had been installed, all in the Pacific. There were________ in the Indian Ocean, and many countries in the region had no national warning centers that could have ________ local communities. That policy mistake had tragic consequences. In Sumatra people had only a few minutes to run, ________the tsunami took two hours to reach India, and some 16,000 people died there. “It was totally unnecessary,” says Paramesh Banerjee, a geo-physicist at Nanyang Technological University in Singapore. “Technically it would have been relatively ________ to install a tsunami warning system for the Indian Ocean.”

There are now 53 detector buoys operating in the world’s oceans, including 6 of a planned 27 in the Indian Ocean. So a (n)________ of the 2004 horror, in which the tsunami traveled for hours and still caught people by ________ is less likely. But buoys would not have helped in Sumatra. People living on coasts near a rupturing fault (地壳断层) can’t wait for ________ that a tsunami is on its way, which it often isn’t; they must flee as soon as the quake hits. The Japanese warning system relies not only on tsunameters but also on seismometers (地震测量仪) — a thousand of them ________ the country, the densest network anywhere — combined with a computer model that forecasts the scale of a tsunami from the magnitude (震级) and ________ of the quake.

In March, the system, which is run by the Japan Meteorological Agency (JMA), did not work perfectly. JMA’s initial ________, while the ground was still shaking, put the quake magnitude at 7.9 — but later analysis revealed a quake that, at magnitude 9, was 12 times larger. The tsunami forecast warned of waves of ten feet or more — but they reached 50 feet in Minanisanriku and in some places even ________. But the human ________ to the warning was imperfect as well. “I think this time many people who lived above the high-water mark of the 1960 tsunami didn’t bother to run.” says Jin Sato, mayor of Minanisanriku. “Many of them died.” The town’s seawall, he thinks, also gave people a false sense of ________

5 . After five long years, it appears California’s drought is finally becoming less severe. _______ a recent string of storms, more than a third of the state has now welcomed healthy precipitation (降水量), and California’s snowpack—a(n) _______ source of water as the year progresses—has reached nearly twice its seasonal average in some parts of the Sierra Nevada. That’s a dramatic improvement over last summer, when literally every inch of the state _______ drought conditions. It’s also welcome news for Californians, who have faced a series of water _______ since Governor Jerry Brown declared a state of emergency in early 2014. Farmers have been forced to spend heavily to maintain production.

The state’s water struggles, _______, are far from over. For one, nobody knows for sure how long these rains will last. Although recent precipitation has been _______—in some places more than 80 inches—the accuracy of storm forecasting remains _______ beyond a week. Californians know this all too well: last year, experts projected a “Godzilla” El Niño that would bring record levels of precipitation. It never _______. “Will six weeks from now be wet?” asks Jeanine Jones, California’s interstate water-resources manager. “The skill in that kind of forecasting is just not there.”

_______, a storm slowdown is a very real possibility—and it could leave California without enough water to make it through the dry summer. ________, when that happens, the state has turned to groundwater stored in natural rock formations deep beneath the earth’s surface. But those ________ remain used up after years of drought; restoring them could take years in some places, says Jones.

The quick inrush of water has also created a(n) ________ balancing act for water managers. Keeping surface reservoirs (水库) filled to the edge protects against the possibility of a sudden dry spell, but it also

For now, though, Jones is focused on planning and ensuring the state’s water supply whatever may happen. “We’re halfway through our wettest season, and conditions have been encouraging,” she says. “I would say we’re ________ optimistic.”

6 . Sea levels along coastlines in the United States will rise about one foot by 2050, with larger increases on the East and Gulf coasts, according to a comprehensive new report by climate scientists.

Oceans have already risen about one foot in the last century, as climate change melts glaciers (冰川) and ice caps around the world. But the pace is ______ scientists warn, and the next 30 years will see the same amount of sea level rise as the previous 100.

The report gives the most concrete and certain sea level ______ ever published for the U.S. And advances in computer models and real-world information about rising seas make it possible to see the future more ______ than ever.

Sea level rise ______ dramatically for different parts of the U.S. coast. The ocean is not like a bucket of water that rises at the same time as more liquid is ______. Ocean ______ push more water into some areas than others. Ice in different regions melts at different rates. In many parts of the world, sea level rise is ______ because coastal land is sinking.

The new report adds up all those factors to give ______ estimates for different parts of the U.S. The authors predict about a foot and a half of sea level rise for the Gulf Coast by 2050, with particular hot spots from Texas to Mississippi, where exploitation of underground oil, gas and drinking water is causing the land to rapidly _____ into the rising ocean water. There are ______ hot spots in the Mid-Atlantic region, including Annapolis, Md. and Norfolk, Va. Overall, the East Coast is ______ to experience a little more than a foot of sea level rise in the next 30 years.

Sea level rise is happening more ______ on the West Coast, including much of southern and western Alaska, the report finds. The authors predict about six inches of sea level rise by 2050.

William Sweet, a sea level rise expert with the National Oceanic and Atmospheric Administration (NOAA) and one of the authors of the new report, says cities that are not yet flooded should ______ now. Quickening sea level rise may require that humans ______ where and how we build homes, offices, roads and anything else that is better dry than wet. Right now, development in flood-prone (易发洪水的) areas is increasing, despite climate change.

Beyond 2050, the report makes clear that humans have a ______: reduce greenhouse gas emissions and control sea level rise, or keep burning fossil fuels and face oceans that are two, three or even 10 feet higher than today.

What Can One City Do?

People around the world are concerned about global warming and are talking about ways to stop it. The city of Cambridge, Massachusetts, in the United States, is doing more than just talking. Cambridge wants to become a world leader in energy-efficient buildings.

Today, Naema Omar is improving her 80-year-old house in Cambridge. To keep the heat inside in the winter, she is filling the space inside the walls with insulation(绝缘). Insulation is usually made from chemicals, but in her house, she is using     1     new - insulation made from recycled blue jeans and other clothes. She has also put in a new type of light called an LED lamp    2     uses only a tiny amount of electricity. The light-bulbs in it last for 20 to 30 years before needing     3     (change).

But eco-friendly insulation and lighting are much more expensive than the usual kind     4     many people in Cambridge can’t afford them. A group called Cambridge Energy Alliance (CEA)     5     (work) to solve this problem. They want to help every resident and business in the city conserve energy. People can ask the group to come and look at     6     they can make their house or office building eco-friendly. The CEA then makes them a plan to save 15 to 30 percent on heating, gas, water, and electricity. Then the group help people borrow money to pay for the improvements. The money that people save by being     7     (efficient) should be enough to pay back the loan.

It was ten years ago that the city of Cambridge decided to try to reduce its carbon emissions. More than 80 percent of the carbon dioxide     8     (produce) in Cambridge comes from buildings - not from cars     9     successful, the program will not only save a lot of energy but also make new jobs for local people. Workers    10     (need) to put in insulation, install better doors and windows, and make other energy improvements on buildings. The CEA hopes that their program will be an example for other cities.

The Mega-City Environment

Mega-cities suffer from a catalog of environmental ills. A World Health Organization(WHO)/United Nations Environment Program(UNEP)study found that seven of the cities-Mexico City, Beijing, Cairo, Jakarta, Los Angeles, Sao Paulo and Moscow-had three or more pollutants that    1     the WHO health protection guidelines. All 20 of the cities studied by WHO/UNEP had at least one major pollutant that went beyond    2     health limits.

According to the World Resources Institute, “Millions of children living in the world’s largest cities, particularly in developing countries, are    3     to life-threatening air pollution two to eight times above the maximum based on WHO guidelines. Indeed, more than 80 percent of all deaths in developing countries    4     to air pollution-induced lung infections are among children under five.” In the big Asian mega-cities such as New Delhi, Beijing and Jakarta, approximately 20 to 30 percent of all respiratory diseases    5     from air pollution.

Almost all of the mega-cities face major fresh water challenges. Johannesburg, South Africa, is forced to draw water from highlands 370 miles away. In Bangkok, saltwater is invading aquifers(地下蓄水层). Mexico City has a serious    6     problem because of excessive groundwater withdrawal.

More than a billion people, 20 percent of the world’s population, live without regular    7     to clean running water. While poor people are forced to pay high fees for private water, many cities squander their resources through leakages and illegal    8    . “With the population of cities expected to increase to five billion by 2025,” says Klaus Toepfer, executive director of the UNEP, “the urban demand for water is set to increase rapidly. This means that any solution to the water crisis is closely linked to the governance of cities.“

Mega-city residents, crowded into unsanitary slums, are also subject to serious disease outbreaks. Lima, Peru(with population estimated at 9.4 million by 2015)suffered a cholera outbreak in the late 1990s partly because, as the New York Times reported, ”rural people new to Lima...live in houses without running water and use the outhouses(屋外厕所)that    9     the hillsides above.“

It’s worth looking at some of these    10     mega-cities in detail, because daily life there is likely to be the pattern for a majority of the world’s population. Most are already experiencing severe environmental problems that will only be worsened by rapid population increases.

10 . The cultivation of plants by ants is more widespread than previously realized, and has evolved on at least 15 separate occasions.

There are more than 200 species of ant in the Americas that farm fungi (真菌) for food, but this trait evolved just once sometime between 45 million and 65 million years ago. Biologists regard the cultivation of fungi by ants as true agriculture appearing earlier than human agriculture because it meets four criteria: the ants plant the fungus, care for it, harvest it and depend on it for food.

By contrast, while thousands of ant species are known to have a wide variety of interdependent relationships with plants, none were regarded as true agriculture. But in 2016, Guillaume Chomicki and Susanne Renner at the University of Munich, Germany, discovered that an ant in Fungi cultivates several plants in a way that meets the four criteria for true agriculture.

The ants collect the seeds of the plants and place them in cracks in the bark of trees. As the plants grow, they form hollow structures called domain that the ants nest in. The ants defecate (排便) at designated absorptive places in these domain, providing nutrients for the plant. In return, as well as shelter, the plant provides food in the form of fruit juice.

This discovery prompted Chomicki and others to review the literature on ant-plant relationships to see if there are other examples of plant cultivation that have been overlooked. “They have never really been looked at in the framework of agriculture,” says Chomicki, who is now at the University of Sheffield in the UK. “It’s definitely widespread.”

The team identified 37 examples of tree-living ants that cultivate plants that grow on trees, known as epiphytes (附生植物). By looking at the family trees of the ant species, the team was able to determine on how many occasions plant cultivation evolved and roughly when. Fifteen is a conservative estimate, says Campbell. All the systems evolved relatively recently, around 1million to 3 million years ago, she says.

Whether the 37 examples of plant cultivation identified by the team count as true agriculture depends on the definitions used. Not all of the species get food from the plants, but they do rely on them for shelter, which is crucial for ants living in trees, says Campbell. So the team thinks the definition of true agriculture should include shelter as well as food.