If you see a house cat, the    1    are high that it will have white paws, a look that many owners affectionately call“socks.” But socks are rarely seen in wildcats, the elusive and undomesticated cousin of the house cat, so why do so many pet cats sport furry white feet?

As it turns out, this story started about 10,000 years ago, when humans and cats     2       life was better together.

This    3    eventually led to uber-prevalent socks on cats, as well as other well-known coat patterns, said Leslie Lyons, professor emerita and head of the Feline Genetics Laboratory at the University of Missouri College of Veterinary Medicine.

“As humans became farmers and started staying in one place, they had grain stores and waste piles” that attracted rodents, Lyons said. It was a mutually beneficial arrangement: the humans had fewer rodents to deal with and the cats got an easy meal.

The wild, undomesticated ancestor species of house cats, Felis silvestris, lives in Africa and Eurasia. These felines are tasty snacks as kittens and stealthy predators as adults, so     4     born with a coat that offers camouflage (保护色) have tended to survive and reproduce.

But not every F. silvestiis is born with a coat that blends into its habitat.

“Genetic mutations are occurring all the time.” Lyons said.

There isn’t much evidence to indicate why early cat people chose the individuals they did, but Lyons said the range of coats seen on modern domestic cats shows that our agrarian ancestors favored cats with markings that would have     5    with their camouflage.

In its native mixed forest or scrub desert environment, a cat with stark white paws would have stood out to predators and prey.

When humans started taking an interest in cats, these white paws would have stood out to them, too. “There were probably people saying, ‘I particularly like that kitten because it has white feet . Let’s make sure it survives’”, Lyons said.

Humans probably also    6    cats who were calm and comfortable around humans, Lyons said. Behavioral traits seem unrelated to coat color, but for reasons that scientists don’t fully understand, white spots tend to appear when the     7    individuals are selected and bred.

These    8    fur colors and markings emerge while a cat embryo is developing. The cells that give cat fur its color first appear as neural crest cells, which are located along what will become the back, Lyons said.

Then, those cells slowly migrate down and around the body. If those waves of cells move far enough to meet each other on the cat’s front side, the embryo will be born a solid-colored kitten, such as an all-black or all-orange cat. Felines     9    white feet, faces, chests and bellies when these cells don’t quite make it all the way.

So, the next time you see a kitty wearing white socks, you’ll know that this     10     feature is a result of genetic mutations, domestication and developmental biology. Although if you try telling the cat that, it will probably just look at you quizzically before sauntering away.

2 . Why we should spare parasites

Growing up, Chelsea Wood dreamed of becoming a marine biologist and studying large, exciting animals like sharks. Instead, she later found herself peering through a microscope at the organs of a snail. She had often plucked snails off rocks and collected them in buckets, but she had never looked inside of one. Seen through the microscope, they are surprisingly charming. “I couldn’t believe that I’d been looking at snails for as long as I had and missing all the cool stuff,” says wood. “I just totally fell in love with them.”

Nearly half of all known animals are parasites. One study projects that a tenth of them may be doomed to extinction because of climate change, loss of their hosts, and deliberate attempts at eradication. Though it seems few people care — or even notice.

    1    . But most parasites have evolved not to kill their hosts, and not all of them even cause noticeable harm to them.

Scientists warn of dire consequences if we continue to ignore the dangerous situation of parasites. Not only are some of them useful to humans [such as medicinal leeches, still employed in some surgeries], but they also play crucial roles in ecosystems, keeping some populations in check while helping to feed others.

Some experts say there’s an aesthetic argument for saving them.     2    . They’ve evolved clever means of survival, from becoming a fish’s tongue to controlling the minds of cockroaches.

We’ve barely begun to identify all the parasites. “That’s just not something that we’ve prioritized,” says Skylar Hopkins, an ecologist at North Carolina State University. So, Hopkins pulled together a group of scientists interested in parasites, and they started sharing what they knew.

Since parasites rely on other species, they can be easily hurt, Take, for example, the endangered pygmy hog-sucking louse. It only lives on another species that is itself endangered, the pygmy hog, which is disappearing fast. Then there’s the California condor louse. In the 1970s, desperate to save the California condor, biologists began raising them in captivity. Part of the protocol was to delouse every bird, on the assumption that parasites were bad for condors, though it’s not clear that they actually were.

While the death of parasites might seem like no big deal, ecologists caution that wiping them out could end up dooming the planet.     3    . Big predators would lose out too. Many parasites move into their next host by manipulating the host they’re in, which drives that host into a predator’s mouth so that the predator can be fed.

Even human health wouldn’t entirely benefit from wiping out parasites. The human immune system evolved alongside a group of parasites, and if we were to kill them off, our immune systems would then began attacking ourselves.

However, scientists aren’t out to save all parasites. The Guinea worm, for instance, should not be spared. It grows inside a person’s abdomen, causing harm to one’s health.

If anyone would want to get rid of all parasites, you’d think it would be Bobbi Pritt. As medical director for the Mayo Clinic’s human parasitology lab, Pritt identifies harmful parasites found all over the country and in every body part. Yet even Pritt has a soft spot for parasites. As a physician, she favors wiping out parasites that cause disease and suffering.     4    .

Ultimately, we do not want a war against all of them, because there’s still so much we don’t understand.

This past July was the hottest recorded month in human history. Heat waves smashed temperature records worldwide and even brought summer temperatures to Chile and Argentina during the Southern Hemisphere’s winter. It’s more than just a matter of sweaty discomfort. In the U.S. alone, it kills more people each year than floods, tornadoes and hurricanes combined. As climate change worsens, access to     1     cooled spaces is rapidly becoming a health necessity.

Yet standard air-conditioning systems have     2     us in a vicious cycle: the hotter it is, the more people use the AC—and the more energy is used as a result. Nicole Miranda, an engineer researching sustainable cooling at the University of Oxford says: “it’s not only a vicious cycle, but it’s a(n)     3     one.” According to 2018 data from the International Energy Agency (IEA), the worldwide annual energy demand from cooling is     4     to more than triple by 2050.

It’s becoming increasingly clear that humans cannot outrun climate change with the same air-conditioning technology we’ve been using. One well-known problem with current AC systems is their reliance on refrigerant     5    , many of which are potential greenhouse gases. About 80 percent of a standard AC unit’s climate-warming emissions currently come from the energy used to     6     it, says Nihar Shah, director of the Global Cooling Efficiency Program at Lawrence Berkeley National Laboratory.

Standard air-conditioning systems     7     cool and dehumidify through a relatively inefficient mechanism: in order to condense water out of the air, they overcool that air past the point of comfort. Many new designs therefore separate the dehumidification and cooling processes, which avoids the need to overcool.

Even with some of the best technologies available, the gains in     8     alone might not be enough to offset the widely expected increase in air-conditioning use. It will not work to simply replace every     9     air conditioner with a better model and call it a day. Instead, a truly cooler future will have to     10     other strategies that rely on urban planning and building design to minimize the need for cooling in the first place.

5 . For millions of years, Arctic sea ice has expanded and shrunk in a rhythmic dance with the summer sun. Humans evolved in this icy world, and civilization relied on it for climatic, ecological and political stability. But now the world comes ever closer to a future without ice. The National Snow and Ice Data Center reported that 2019’s minimum arctic sea ice extent was the second lowest on record. Arctic summers could become mostly ice-free in 30 years, and possibly sooner if current trends continue. As the northern sea ice declines, the world must unite to preserve what remains of the Arctic.

Although most people have never seen the sea ice, its effects are never far away. By reflecting sunlight, Arctic ice acts as Earth’s air conditioner. Once dark water replaces brilliant ice, Earth could warm substantially, equivalent to the warming caused by the additional release of a trillion tons of carbon dioxide (CO₂) into the atmosphere and declining sea ice threatens wildlife, from the polar bear to algae that grow beneath the sea ice, supporting the large amount of marine life.

To avoid the consequences the scientific community should advocate not just for lowering greenhouse gas emissions, but also for protecting the Arctic from exploitation. The Antarctic shows the way. In the 1950s, countries raced to claim the Antarctic continent for resources and military installations. Enter the scientists. The 1957-1958 International Geophysical Year brought together scientists from competing countries to study Antarctica, and countries temporarily suspended their territorial disputes (争议). In 1959, 12 countries signed the Antarctic Treaty to preserve the continent for peaceful scientific discovery rather than territorial and military gain.

Sixty years later, we must now save the Arctic. A new Marine Arctic Peace Sanctuary (MAPS) Treaty would protect the Arctic Ocean as a scientific preserve for peaceful purposes only. Similar to Antarctica, MAPS would prohibit resource exploitation, commercial fishing and shipping, and military exercises. So far, only 2 non-Arctic countries have signed MAPS; 97 more need to sign on to enact it into law. Scientists can help—just as they did for the Antarctic—by giving statements of support, asking scientific organizations to endorse (支持) the treaty, communicating the importance of protecting the arctic to the public and policy-makers, and above all, by convincing national leaders to sign the treaty. In particular, Arctic nations must agree that recognizing the arctic as an international preserve is better than fighting over it. In 2018, these countries successfully negotiated a 16-year moratorium on commercial fishing in the Arctic high seas, demonstrating that such agreements are possible.

Humans have only ever lived in a world topped by ice. Can we now work together to protect Arctic ecosystems, keep the northern peace, and allow the sea ice to return?

A rare hole has opened up in the ozone layer above the Arctic, in     1     scientists say is the result of unusually low temperatures in the atmosphere above the north pole.

The hole has reached record dimensions, but is not expected to pose any danger to humans     2     it moves further south.     3     it extends further south to overpopulated areas, such as southern Greenland, people will be at increased risk of sunburn. However, on current trends the hole is expected to disappear altogether in a few weeks.

Low temperatures in the northern polar regions led to an unusual stable polar vortex (极地漩涡), and the presence of ozone-destroying chemicals such as chlorine (氯) in the atmosphere - from human activities-caused the hole     4     (form) .

It is now too early to say     5     the unusually stable Arctic polar vortex conditions are linked with the climate crisis, or part of normal stratospheric weather variability. Peuch said there were no direct implications for the climate crisis. Temperatures in the region are already increasing,     6     (slow) the destruction of ozone.

    7     a hole over the Arctic is a rare event, the much larger hole in the ozone layer over the Antarctic has been a major cause for concern for more than four decades. The production of ozone-destroying chemicals     8     (reduce) dramatically, under the 1987 Montreal Protocol (蒙特利尔协议) , but some sources appear still to be functioning.

New sources of ozone-destroying chemicals were not a factor in the hole     9     (observe) in the Arctic, said Peuch. “However, this is a reminder that one should not take the Montreal Protocol measures for granted, and that observations from the ground and from satellites are central to avoiding a situation     10     the ozone-destroying chemical level in the stratosphere could increase again.”

10 . What is the Great Pacific Garbage Patch?

The Great Pacific Garbage Patch (GPGP) is the largest of the five offshore plastic accumulation zones in the world’s oceans. It is located halfway between Hawaii and California.

PLASTIC __________

It is estimated that 1.15 to 2.41 million tonnes of plastic are entering the ocean each year from rivers. More than half of this plastic is less __________than the water, meaning that it will not sink once it encounters the sea.

The strong and floating plastics show resiliency(韧性) in the marine environment, allowing them to be transported over __________distances. They persist at the sea surface as they make their way off shore, transported by converging (汇聚的) currents and finally accumulating in the patch.

Once these plastics enter the gyre（环流）, they are unlikely to leave the area until they __________into smaller microplastics under the effects of sun, waves and marine life. As more and more plastics are discarded into the environment, microplastic __________in the GPGP will only continue to increase.

LOCATION

Due to seasonal and interannual variabilities of winds and currents, the GPGP’s location and shape are constantly changing. Only floating objects that are __________influenced by currents were likely to remain within the patch.

By simulating concentration levels in the North Pacific, the researchers were able to follow the location of the patch and found on average it orbits around 32°N and 145°W. However, the team observed seasonal __________from west to east and substantial variations in latitude（纬度）depending on the year.

IMPACT ON WILDLIFE

Plastic has increasingly become a very common substance in the ocean. Due to its size and color, animals __________the plastic for food, causing malnutrition; it poses entanglement（缠绕）risks and threatens their overall behavior, health, and existence.

Studies have shown that about 700 species have encountered marine debris, and 92% of these __________are with plastic. 17% of the species affected by plastic are on the International Union for Conservation of Nature Red List of Threatened Species.

IMPACT ON HUMANS AND SOCIETY

Once plastic enters the marine food web, there is a possibility that it will contaminate the human food chain as well. Through a process called bioaccumulation, chemicals in plastics will enter the body of the animal __________on the plastic, and as the feeder becomes prey, the chemicals will pass to the __________—making their way up the food web that includes humans. These chemicals that affected the plastic feeders could then be __________within the human as well.

__________, yearly economic costs due to marine plastic are estimated to be between $6-19billion USD. The costs __________its impact on tourism, fisheries and aquaculture, and governmental cleanups. These costs do not include the impact on human health and the marine ecosystem due to __________research available.