2022 年 12 月大学英语六级考试真题（第 3 套）

American colleges and universities are using 64 percent less coal than they did a decade ago, burning 700,000 tons last year, down from 2 million tons in 2008, the U. S. Energy Information Administration (EIA) said in a report __26__ yesterday.

All 57 schools that were burning coal in 2008 are using less now, and 20 have __27__ coal completely, EIA found.

Most universities have turned to natural gas as a __28__, with state funding backing the fuel switch.

While academic institutions use less than 0.1 percent of U.S. coal burned for power, campus coal use has a history dating back to the 1800s when __29__ to power was scarce.

Many universities still operate their own power plants. The Public Utility Regulatory Policies Act of 1978 encouraged more electricity generation by allowing institutions to sell __30__ power to utilities.

But EIA noted many coal-fired universities have signed onto the American College and University Presidents Climate Commitment, which was launched in 2007.

About 665 schools are part of the program, which aims to __31__ greenhouse gas emissions. Thirty percent of the participants have pledged to be carbon __32__ within 20 years.

The Sierra Club's Beyond Coal campaign, which also leads campaigns for universities to withdraw their __33__ in coal and other fossil fuels, lists 22 schools that have pledged to move "beyond coal," including Clemson University, Indiana University, Ohio University, Penn State University, the University of Louisville and the University of Tennessee, Knoxville.

The largest coal use __34__ at colleges were in Michigan, Missouri, Tennessee and Indiana. Indiana's universities alone cut coal __35__ by 81 percent between 2008 and 2015.

During the same period, Michigan made an 80 percent cut and Tennessee cut back by 94 percent at state institutions.

How can one person enjoy good health, while another person looks old before her time? Humans have been asking this question for thousands of years, and recently, it's becoming clearer and clearer to scientists that the differences between people's rates of aging lie in the complex interactions among genes, social relationships, environments and lifestyles. Even though you were born with a particular set of genes, the way you live can influence how they express themselves. Some lifestyle factors may even turn genes on or shut them off.

Deep within the genetic heart of all our cells are telomeres, or repeating segments of noncoding DNA that live at the ends of the chromosomes (染色体). They form caps at the ends of the chromosomes and keep the genetic material together. Shortening with each cell division, they help determine how fast a cell ages. When they become too short, the cell stops dividing altogether. This isn't the only reason a cell can age—there are other stresses on cells we don't yet understand very well, but short telomeres are one of the major reasons human cells grow old. We've devoted most of our careers to studying telomeres, and one extraordinary discovery from our labs is that telomeres can actually lengthen.

Scientists have learned that several thought patterns appear to be unhealthy for telomeres, and one of them is cynical hostility. Cynical hostility is defined by high anger and frequent thoughts that other people cannot be trusted. Someone with hostility doesn't just think, "I hate to stand in long lines"; they think, "Others deliberately sped up and beat me to my rightful position in the line!" and then get violently agitated. People who score high on measures of cynical hostility tend to get more heart disease, metabolic disease and often die at younger ages. They also have shorter telomeres. In a study of British civil servants, men who scored high on measures of cynical hostility had shorter telomeres than men whose hostility scores were low. The most hostile men were 30% more likely to have short telomeres.

What this means: aging is a dynamic process that could possibly be accelerated or slowed—and, in some aspects, even reversed. To an extent, it has surprised us and the rest of the scientific community that telomeres do not simply carry out the commands issued by your genetic code. Your telomeres are listening to you. The foods you eat, your response to challenges, the amount of exercise you get, and many other factors appear to influence your telomeres and can prevent premature aging at the cellular level. One of the keys to enjoying good health is simply doing your part to foster healthy cell renewal.

Scientists have created by accident an enzyme (酶) that breaks down plastic drinks bottles. The breakthrough could help solve the global plastic pollution crisis by enabling for the first time the full recycling of bottles.

The new research was spurred by the discovery in 2016 of the first bacterium that had naturally evolved to eat plastic at a waste dump in Japan. Scientists have now revealed the detailed structure of the crucial enzyme produced by the bug.

An international team then adjusted the enzyme to see how it had evolved, but tests showed they had accidentally made the molecule even better at breaking down the plastic used for drinks bottles. "What actually turned out was we improved the enzyme, which was a bit of a shock," said head researcher Prof. McGeehan, at the University of Portsmouth, UK.

Currently, the enzyme takes a few days to start breaking down the plastic, far faster than the centuries it takes in the oceans, but the researchers are optimistic this can be speeded up even further and become a viable large-scale process.

"What we are hoping to do is use this enzyme to turn this plastic back into its original components, so we can literally recycle it back to plastic," said McGeehan. "It means we won't need to dig up any more oil and, fundamentally, it should reduce the amount of plastic in the environment."

About 1 million plastic bottles are sold each minute around the globe and, with just 14% recycled, many end up in the oceans where they have polluted even the remotest parts, harming marine life and potentially people who eat seafood. "Plastic is incredibly resistant to degradation," said McGeehan. "It is one of these wonder materials that has been made a little bit too well."

Currently those bottles that are recycled can only be turned into opaque fibres for clothing or carpets, while the new enzyme indicates a way to recycle old clear plastic bottles back into new clear plastic bottles.

"You are always up against the fact oil is cheap, so plastic is cheap," said McGeehan. "It is so easy for manufacturers to generate more of that stuff, rather than even try to recycle, but I believe there is a public interest here: perception is changing so much that companies are starting to look at how they can properly recycle these bottles."

Prof. Adisa Azapagic, at the University of Manchester in the UK, agreed the enzyme could be useful but added: "A full life-cycle assessment would be needed to ensure that the technology does not solve one environmental problem- waste- at the expense of others, including additional greenhouse gas emissions."