Walk down the drinks section at the supermarket.Look in the drink cooler in your local convenience store.A new drink is taking up more and more space on the shelves，and that drink is water.Bottled water sales in the US rose to 1.7 billion gallons in 2010 for plastic bottles alone，compared to total sales of only 700 million gallons in 1990. Whereas bottled water was once associated only with the rich and the privileged (特权阶层)，it is now regularly drunk by people at all income levels despite the fact that the price of bottled water can be between 240 and 10,000 times higher per gallon than tap water.What accounts for this surprising increase in demand?

    Traditionally，people have drunk bottled water for health reasons.The practice of “taking the waters” originated with the Romans，who believed that a person developed a healthy mind by building a healthy body.Across Europe，drinking or bathing in mineral water has been associated with the power to cure various diseases.Health spas at Evian in France and Pellegrino in Italy began bottling water so that their consumers could continue their treatments at home.The consumers in the 21st century are also concerned about health.However，in America，where the habit of drinking bottled water is relatively new，the concern is often more related to the purity or sterilization (消毒) of the water than to its mineral contents.Americans are often worried about the effects of the chemical pollution and other contaminants on the water supply.Many Americans view bottled water as a safe alternative to tap water.

    Further reasons for drinking bottled water are its usefulness as an aid to digestion，as a complement to a good meal in a restaurant，and for taste.City tap water is often treated with chlorine (氯) to guard against harmful micro­organisms.Chlorine，as well as metals from pipes and tanks used to distribute and store tap water，can leave behind an unpleasant taste.

Four apps for students to learn English

    Quizlet

    Quizlet is a learning app—a computer program you use on your mobile device. It can help users build and test their knowledge of English words and terms. Quizlet has word sets for millions of subjects. And, it is quickly becoming a useful mobile tool for language learners.

    Socrative

    In Socrative, teachers can create timed learning games. In class, students compete individually or as part of a team against classmates. One game students love is called space Race. In this game, if a team answers a question correctly, their rocket moves forward. This team whose rocket gets to the end first wins. Also, teachers can use Socrative as an “exit ticket, ”a question they can ask students about what they learned in that day's class. Students write their answers on their mobile devices. Then, the teacher can show the answers on a shared video screen.

    QR Codes

    AQRCodeisakindofsignthatasmartphonecanreadwithitscamera. When your phone camera reads a QR code, it takes you to a website, image, video or anything you want to share. For example, one will take you to the VOA Learning English website.

    Evernote

    Evernote lets users store and share notes, images and recordings in one place. Teachers can also use Evernote to give homework.

    After shopping for deals in stores on "Black Friday", or online on "Cyber Monday", Americans and people worldwide are preparing for newly popular "Giving Tuesday". Starting in 2012, now the global event that is celebrated annually on the Tuesday after Thanksgiving is the brainchild of 92nd Street Y, a cultural center in New York City and United Nations Foundation.

    As the name indicates, Giving Tuesday is meant to restart the charitable season and therefore observed by raising funds for local nonprofits and schools, organizing food and clothing drives, and conducting random acts of kindness. In 2015, 700, 000 people from 71 countries came together to donate $116.7 million in cash. An additional $1.08 million was spent on gifts.

    While the easiest way to participate is by donating to your favorite charity, this day can be celebrated in many other ways too. You can give back by volunteering at your local shelter or food bank, or even by donating blood. If all else fails, a purchase from the growing number of organizations that give a portion of their sales to charity will do the trick.

    But perhaps the best way to celebrate the day is by helping those nearest and dearest to you. Assist a family member with a simple chore like folding laundry, cooking dinner, or even reading to a younger sibling. No matter what you do, be sure to share you good deed on social media and inspire others to celebrate Giving Tuesday as well!

    Breathing dirty air comes at a high price. Air pollution lowers the average life spans (寿命) by a year worldwide and in more polluted parts of Asia and Africa, dirty air shortens lives up to twice that much. Scientists shared their new findings in Environmental Science & Technology Letters. The study used data gathered in 2016 as part of a project known as the Global Burden of Disease and was the first major country-by-country look at the connection between the length of life and what's known as fine PM.

    Air pollution has been linked to many health problems. Most earlier studies had looked at how tiny air pollutants affected rates of illness or death. Joshua Apte is an environmental scientist at the University of Texas at Austin. By looking at life expectancy (预期寿命), his team had hoped to make the threat easier to understand. PM2.5 is what scientists call tiny particles (颗粒) of pollution in the air. Higher levels of PM2.5 can cause health problems and cut months, if not years, from the average length of life. This analysis shows how pollution affects life expectancy in different parts of the world.

    The World Health Organization (WHO) recommends limiting PM2.5 to 10 micrograms per cubic meter of air. Apte's group calculated how holding pollution to this low level would help people. In countries with very dirty air, meeting this standard would lengthen people's lives. However, in countries whose air already meets this standard, the study shows no gain in life expectancy. In other words, meeting the WHO standard won't reduce health costs resulting from dirty air because even below 10 micrograms per cubic meter, pollution still causes serious risks. Meanwhile, the scientists compared how other threats including smoking and cancer shorten the length of life across the globe.

A 293-million-mile journey of the NASA Perseverance rover (探测器) to Mars: ended successfully on February 18, 2021, with a picture-perfect landing inside the Jezero Crater. The car-sized, six-wheeled rover, nicknamed Percy is the US space agency's biggest and most advanced explorer to date. Its primary mission is to search for signs of ancient microbial (微生物的) life on Mars.

Landing on Mars is extremely tricky. The Red Planet's gravitational pull causes approaching spacecraft to go faster to high speeds, while its thin atmosphere-just 1 percent that of Earth's-does little to help slow it down as it approaches the surface.

The scientists had to reduce Percy's 12,000 mph speed to a safe landing speed of less than five mph-in just six and a half minutes. The target entry angle also had to be a precise 12 degrees-any steeper, and the spacecraft would burn up; any flatter, and it would get lost in space. It is no wonder that the final approach is often referred to as the "seven minutes of terror. "

Upon attaining a manageable speed, Percy briefly flew over the Martian surface to seek out the perfect landing spot. Its complex map-reading system rapidly scanned the area and matched it with maps in its database to find the best location.

The NASA scientists will spend the next two months testing Percy's scientific instruments. Once ready, the rover will begin to carry out its mission.

"Perseverance is the smartest robot ever made, but confirming that microbial life once existed carries an unusually large burden of proof," said Lori Glaze, director of NASA's Planetary Science Division. "While we'll learn a lot with the great instruments we have aboard the rover, it may very well require the far more well-equipped laboratories and delicate instruments back here on Earth to tell us whether our samples (样本) carry evidence that Mars once harbored life. "

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