1 . In a bustling city in Arizona stood a high school where most of the students live in poverty. Among them were four sons of Mexican immigrants, Juan, Oscar, Luis, and Alfredo. These boys, coming from ________ backgrounds, often found themselves overlooked and underestimated. Bonded by fate and friendship, they shared a common passion for ________. Two science teachers there decided to enter their high school into a complicated ________ robotics competition sponsored by the NASA and the Naval Research. Excited for the news, these four boys signed up for the competition.

With enthusiasm and energy, they started calling mechanical engineers for design help. They were ________ that these kinds of robots require glass syntactic flotation foam, a type of floating material used in various marine applications.________ money, all they could afford was some PVC pipes and duct tape (强力胶布).________, they searched the city for various spare parts, gathering whatever they could to bring their vision to life. With the teachers’ guidance and encouragement, they ________ together a robot with no more than metal and wires.

As they worked on their robot, the boys also faced personal challenges. Juan struggled with the weight of family responsibilities; Oscar ________ a deep-seated fear of failure; Luis’s heart ached from the constant peers’ mockery (嘲笑) for his ________ accent, and Alfredo longed for acceptance and belonging.________ these obstacles, they persevered, leaning on each other for support and inspiration.

After a few test runs of their robot, they piled into a second-hand van to head to the competition. Upon entering the main pool area, they noticed the college teams wearing matching outfits, with robots sponsored by big companies. Feeling a bit nervous, the boys put the robot in the water for a test run.________, the PVC didn’t hold up, causing the robot to leak and sink.

However, instead of letting this ________ ruin their spirits, the boys put their heads together and came up with a brilliant solution. 12 hours later, armed with 8 super-absorbent pads to plug the leak, the robot was ________ into the pool again. This time, their robot performed admirably. Gliding gracefully through the waters, it navigated the course with precision and speed,________ the judges and audience alike. This underwater robot, a symbol of their determination and ________, conquered the waters, defeated engineering powerhouse MIT and ranked first in the country. This was not just a win for those four but a victory for every underdog with a dream.

3 . Like anything built by evolution, the human body has many downsides, teeth without exception. Adult humans only get one set of teeth, which must last about 60 years. However, a(n) ________ of poverty, sugar-rich diets and poor hygiene means 2.5bn people globally suffer from tooth decay, in which acid produced by mouth-living bacteria eats away the hard enamel (牙釉质) that ________ the outside of a tooth, leading to further infection and damage. Once decay has set in, all a dentist can do is to fill the gap with artificial filling.

But in a paper published in Cell, Hannele Ruohola-Baker, a stem-cell biologist at the University of Washington, and her colleagues offer a possible ________. Stem cells have the ________ to turn themselves into any other type of cell in the body. It may soon be possible, the researchers claim, to use those ________ cells to regrow a tooth’s enamel naturally.

The first step was to work out how enamel is produced. As enamel-making cells, known as ameloblasts, disappear soon after a person’s adult teeth have finished growing, the researchers ________ samples of tissue from human foetuses (胚胎), which contain plenty of functioning ameloblasts. ________, they checked to see which genes were especially active in the enamel-producing cells. It turned out that genes designed to bind to calcium were particularly busy.

________ that information, Dr Ruohola-Baker and her colleagues next checked to see whether the stem cells could be persuaded to ________ ameloblasts. The team devised various drugs designed to activate the genes expressed in functioning ameloblasts. That worked, with the engineered ameloblasts producing the same proteins as the natural sort.

For now, the work is more concept than a medical treatment. The next step is to boost enamel production further, with a view to ________ beginning clinical trials. The hope is that, one day, medical versions of the team’s findings could be used as biological implants, to ________ a patient’s decayed teeth.

Stem-cell-based therapies are not the only ones heading to clinical trials. Another treatment, known as biomimetic repair, involves rebuilding the tooth crown using synthetic (人工合成的) proteins, which are similar, but not quite ________, to human enamel. The proteins could be included in toothpaste and even cough drops. But synthetic formulations can be less ________ than human enamel.

It will take time for either technology to become reality. One question is how durable the enamel made by stem-cell-derived ameloblasts is. Another is how best to deliver the stem cells to a patient’s mouth. But these findings are ________. As any dentist will tell you, prevention is better than cure. ________, a better cure would be always welcome. There is no doubt that this research offers a new prospect for future dental care.

5 . One summer midnight several years ago, standing outside a wooden cabin in Michigan River, I looked up. The sky was filled with thousands of stars, the sight of which was almost enough to make me, a non-believer, offer a word of ___________ up into the star-filled sky. But to whom? Perhaps to Johan Eklof, author of The Darkness Manifesto.

As a bat scientist, Eklof’s work on bats requires a specific kind of darkness—the ___________kind, unpolluted by light. But this category of darkness is ___________. In the 1980s, Eklof tells readers, two-thirds of the churches in Sweden’s southwest housed bat colonies. Not any longer. “Today, forty years later, research I’ve done with my colleagues shows that this number has been reduced by a third, ___________ light pollution and other factors. Because the churches are all ___________ like carnivals(嘉年华) in the night,” he writes. “We are surrounding ourselves with light.”

Excess light is incredibly ___________ to the complex eco-systems nocturnal (夜间活动的) animals inhabit. It ___________ away the bats that Eklof studies. It frightens light-sensitive moths, leaving them easily ___________ to predation(捕食) or flying endlessly into lights that will never return their love. Baby turtles crawl away from the shoreline toward the lights of distant coastal cities and reef fish eggs go unhatched. Birds do not migrate ___________ and even they forget to sing. Modern advancements such as LED lights could significantly reduce some of the worst impacts, but they have not. At least, not yet.

It is worth mentioning that middle-aged writer like Eklof can ____________ for a darker world — for darkened campuses and unlit parking lots. But darkness is not safe for everyone. We need to address the social issues that make lighted places so ____________ in the first place.

The bottom line: We can change if we want to. Some of the solutions to light pollution— motion-detecting lights, shielded lights that do not ____________ light upward, artificial light with wavelengths that is similar to natural light—are already within our grasp, if we just ____________ them. “We could just turn it all off, but I guess we don’t want to,” said Eklof in a recent interview. “____________, it’s vital we find a middle way.”

Right now it is hard to know what that middle way might look like. In 50 years, every city could be equipped with an array of programmed and ____________ low-impact LED lights. Or we might have completely forgotten what darkness is—the sky filled with little moons.

6 . China becomes a world leader in clean technology by fighting environmental pollution, sharing experience.

Erik Solheim, former executive director of the United Nations Environmental Programme, said he is __________ with China’s phenomenal achievements over the past decade in fighting environmental pollution and climate change, and in its march toward __________ development.

This is very __________ to his Twitter followers. Solheim’s latest tweets include one about China ranking first globally in planted forests and forest coverage growth, __________ a quarter of the world’s new forests in the past decade; one about China producing 60 percent of global solar energy last year and 80 percent of solar panels; and another highlighting the fact that 80 percent of the world’s new offshore wind capacity was installed in China last year.

He believes that it’s time for the rest of the world to __________.

For Solheim, who is also the former Norwegian Minister of the Environment and Minister of International Development, China’s achievements on the climate and environmental fronts all started with its fight against__________.

“People wanted to see beautiful skies over their cities,” he told China Daily. “The __________ fast reduction in air pollution in Chinese cities over the last decade shows how fast China can act. This has now spilled over into renewable energy, nature protection, electric mobility, tree planting and a lot more. Today, China is the world leader in all __________ technologies.”

The latest __________ from China’s Ministry of Ecology and Environment prove Solheim’s observations that the country is rapidly switching to a more sustainable path.

Minister of Ecology and Environment Huang Runqiu told a news conference on Sept 15 that the country’s toughest measures and greatest progress on the ecological and environmental front have occurred in the last decade.

He said that __________ painstaking efforts to combat pollution, clear waters and blue skies have become more commonplace.

While poor air quality used to be a source of frequent public complaints, the average __________ of hazardous airborne PM2.5 particles dropped from 46 to 30 micrograms per cubic (立方的) meter between 2015 and last year.

About 87.5 percent of days last year were rated as having good air quality, up 6.3 percentage points from 2015, making China the country with the biggest __________ in air quality in the world.

In the last decade, the __________ of water at or above Grade III in the country’s five-tier water quality system rose 23.3 percentage points to 84.9 percent, close to the levels in developed countries. Carbon intensity, or carbon emissions per unit of GDP, has declined by 34.4 percent, with coal __________ for 56 percent of total energy consumption, compared to 68.5 percent a decade ago.

China has has legislated or revised roughly 30 laws and regulations, some of which focused on water resource protection, including the Water Pollution Prevention and Control Law, which was modified in 2017, and the Yangtze River Protection Law, which __________ last year.

7 . Once just a science fiction idea, VR (Virtual Reality) has now become more accessible than ever. Wear a pair of VR glass which is connected to your computer and you can_______ a lot of things without stepping out of the room. From climbing the highest mountain in the world to flying a spacecraft, the things you can do with VR are _______.

This new ‘_______’ is becoming more and more popular China. The Report on Chinese VR Users’ Behavior was released on March 18. The report is _______ a survey of 5,626 people, aged between 15 and 39, from across the country. It shows that up to 68.5 percent of people have heard of or are _______ in VR products.

But surprisingly, it isn’t _______ technology that has made VR so popular. “VR has been around for many years, but it will stick this time because there’s enough computer power and the price will just keep _______,” Todd Richmond, a VR group member with the Institute of Electrical and Electronic Engineers in the US, told USA Today.

VR is expected to change various different fields. _______, VR could be used to treat patients with acrophobia (恐高症) by making them think they were standing on top of a high building, or train pilots and miners _______ they had to actually risk their lives in highly dangerous working environments.

“If you have perfect virtual reality, ________ you’ll be able to simulate everything that a human can imagine, it’s ________ to predict where you go from there,” Palmer Luckey, the inventor of the Oculus VR goggles, told NPR.

But the technology is still ________ perfect. Users report feeling motion sickness, headaches and other________while wearing VR glass. Also, ________ more and more tools are flooding the market, the software that runs VR games and simulators has yet to catch up with all the new advancements. It could take a while for VR to be ________ accepted.

When every new technology is first introduced, the technology itself is the driving force. But for it to really blend into people’s lives, meeting basic and practical needs should be the main aim.

9 . According to a survey conducted by wenjuan.com for the China Youth Daily, 71.0 percent of the 1,538 people polled said they watched short videos on a________basis. 61.8 percent believed that long-term viewing of short videos could interfere with their normal social interactions; and 65.2 percent suggested that video platforms step up in issuing regular________so that users could take a break.

This appeal for external aids to help________ the addictive habit hints at the crushing hold short videos have on the shiftless majority— many of them are not utterly ________ self-control in other circumstances.

Another recent survey of juveniles found 65.6 percent of them have watched short videos, and 20 percent of them just couldn’t stop watching.

For as you click on those seemingly________videos, your life will be thrown into a mindless spiral (螺旋)as we eagerly move from one piece to the next, each lasting 20 to 30 seconds, and are shocked, amused, and outraged in rapid________.

You never have a chance to get________, for you are always curious about what the next piece would be like,________more. All that is needed is a slight twitching (抽动) of one of your fingers.       

Respondents do believe some videos could be useful by teaching you how to cook， how to apply make-up, practice wellness, or buy things. There was even an alleged (声称但未经证实的) telecom fraudster publicizing his________and daring the police to catch him in Dubai, according to him.

It is shocking to realize that a published video itself would have ________ acquired a degree of authenticity and enough to prevent all intentions and the need for checking, even________ such basic facts as authorship.

So it is natural that 36.7 percent of the respondents in the wenjuan.com survey cited the issue of false and misleading content in short videos as an issue, and relevant authorities should have stepped in long ago to________it.

Yes, juvenile-only modes have been________for some time, but it is so easy for children to avoid this.________ , there is an equal need for a mechanism to prevent adults from becoming addicted, notably by limiting the lime they are allowed to view the videos. Thus, when 37.0 percent of the respondents said that, as far as viewing habits are concerned, parents should be a role model to prevent the imitation of juveniles. Maybe all parents should________their mobile phones for a moment of self-reflection.