You may think that light pollution isn't something extraordinarily important. You may believe that every other type of pollution has a larger impact on the environment that light pollution does. But light pollution is serious.

    Light pollution, or “sky glow”, is the glow you can see at night above cities and towns. Light pollution is a problem that has been accompanying man ever since he started his first fire some 15,000 years ago. Light pollution is the light that comes from streetlights, buildings, parking lots and any other source of light that is reflected or directed into the atmosphere.

    Urban light pollution means that one-fifth of the world's population can no longer see the Milky Way(银河) with the naked eye(肉眼). Many city kids, even if they did look through the orange smog above their heads, would probably see only a handful of stars. We have lost our view of the stars, and we have mucked up our  night-time environment as well. Astronomers are calling for the dark places on Earth to be preserved as national parks.

    Lots of people find the ever-brightening night annoying, and animals that are programmed to prefer the dark may avoid a brightened habitat. Sea turtles can get lost searching for a beach to lay eggs, and their hatchlings(孵化的幼仔)may confuse over-lit beachfront resorts(度假胜地) for the ocean horizon, wasting precious energy needed to find the sea and escape predators(食肉动物). Because their necks aren't yet long enough to see things far away, baby turtles rely on the mirror image of the moon to guide them to the sea, to begin their new life. A car may even hit a particular turtle, which was thinking the light from a nearby city was moonlight reflecting off the ocean waves. Birds that live in and around cities can die because of sky glow, too. The bright lights can blind them, leading to countless collisions with buildings and other tall structures.

    On an individual level, people can help reduce much sky glow by using lighting only when necessary. The stars above us are priceless heritage— for not only for astronomers but for all humans. More of our children should be able to look up at night and see the Milk Way.

Music

    Opera at Music Hall: 1243 Elm Street. The season runs June through August, with additional performances in March and September. The Opera honors Enjoy the Arts membership discounts. Phone: 241-2742. http://www. cityopera.com.

    Chamber Orchestra: The orchestra plays at Memorial Hall at 1406 Elm Street, which offers several concerts from March through June. Call 723-1182 for more information. http://www.chamberorch.com.

    Symphony Orchestra: At Music Hall and Riverbend. For ticket sales, call 381-3300. Regular season runs September through May at Music Hall and in summer at Riverbend. http://symphony.org/home.asp

    College Conservatory of Music (CCM): Performances are on the main campus (校园) of the university, usually at Patricia Cobbett Theater. CCM organizes a variety of events, including performances by the well-known LaSalle Quartet, CCM's Philharmonic Orchestra, and various groups of musicians presenting Baroque through modern music. Students with I.D. cards can attend the events for free. A free schedule of events for each term is available by calling the box office at 556-4183. http://www.ccm.uc.edu/events/calendar.

    Riverbend Music Theater: 6295 Kellogg Ave. Large outdoor theater with the closest seats under cover (price difference). Big name shows all summer long! Phone: 232-6220. http://www.riverbendmusic.com.

根据短文内容，选择最佳答案，并将选定答案的字母标号填在题前括号内。

    Put technology in the hands of someone like Elon Musk and it can send people into space, make a future of clean and renewable energy a reality, or build electric cars. Put in your hands, and it can help you achieve all sorts of things, from learning to code to learning a language.

    Educational apps are becoming increasingly popular as a supplement(补充), and sometimes as an alternative(替代物), to traditional education. Why? Well, for starters, it's extremely convenient to learn on a pocket-sized device that you already carry around with you at all times. The best apps are also highly interactive and adaptive, coaxing you in and getting you hooked on learning.

 But apps, just like textbooks and language lessons, are a medium through which a language can be studied. The way you use them will affect how successful you are. If you flick through a textbook and don't dare say a word in your language lessons, you'll make slow progress. The keen reader who repeats each exercise in the textbook and engages the teacher in the conversation will move ahead. So how do you ensure you get the most out of your app, and what should you consider before you install(安装) one?

    Before that, a very quick introduction: I developed the following five points from my experience as both a language teacher and learner, and from working in startups in the field of language. I spent six years teaching in Germany and Spain as well as developing a video learning startup. However, I first came to language learning late. I started learning Spanish at 22, and was able to use Spanish and German freely by about 28. I've been using language apps for the last few years, and participated in two successful one-week challenges to go from zero to hero in Italian and French. If you're interested, you can see the French challenge here.

    So, just before downloading an app, here's what you should think about…

    Alexa is a form of artificial intelligence, or AI for short. Many people start their mornings by asking Alexa for the weather forecast or the latest news. A device(设备) that houses Alexa can also play music from your favorite playlists, keep a shopping list, order takeout food, answer questions, send messages and even run “smart” home controls.

    Training AI systems to respond to problems with human-like intelligence and learn from their mistakes can take months, or even years. Consider Alexa and similar software, such as Apple's Siri. To do the tasks its human owners ask, these systems must make sense of and then respond to sentences such as, “Alexa, play my Ed Sheeran playlist” or “Siri, what is the capital of India?”

    Computers can't understand language as it is spoken by people. So AI researchers must find a way to help humans communicate with computers. The technology used to get computers to “understand” human speech or text is known as natural language processing. By natural language, computer scientists refer to the way people naturally talk or write. To teach an AI system a task like comprehending(理解) a sentence or responding to a person 's last move in a board game, scientists need to feed it lots of examples.

AlphaGo is an AI system designed by Google that has beaten a human champion, Lee Sedol, at the strategy(策略) board game Go. To train AlphaGo, Google had to show it 30 million Go moves that people had made while playing the game. Then AlphaGo used what it learned to analyze those plays as it played against different versions (版本) of itself. During this practice, the program came up with new moves—ones never seen in games between people.

    What happens inside the head of a soccer player who repeatedly heads a soccer ball. That question motivated a study of the brains of experienced players.

    Researchers at the Albert Einstein College of Medicine in New York selected 34 adults, men and women. All of the volunteers had played soccer since childhood and  now competed year﹣round in adult soccer leagues. Each filled out a detailed questionnaire developed especially for this study to determine how many times they had headed a soccer ball in the previous year, as well as whether they had experienced any known concussions in the past.

    Then the players completed computerized tests of their memory and other learning skills and had their brains scanned. using a complex new M.R.I. technique which can find structural changes in the brain that can't be seen during most scans.

    According to the data they presented, the researchers found that the  players who had headed the ball more than about 1, 100 times in the previous 12 months showed significant loss of white matter in parts of their brains involved with memory, attention and the processing of visual information, compared with players who had headed the ball less.

    This pattern of white matter loss is "similar to those seen in traumatic brain injury", like that after a serious concussion, the researchers reported, even though only one of these players was reported to have ever experienced a concussion.

    The players who had headed the ball about 1, 100 times or more in the past year were also generally worse at remembering lists of words read to them, forgetting the words far more often than players who had headed the ball less.

    A young woman turns around and around quickly, and jumps high. In the background, a young girl reads a rejection (拒绝) letter from a ballet school. "You have the wrong body for ballet," it says, "and at thirteen, you are too old." This was one of the most popular advertisements (广告) of 2014 and it describes American ballet Theatre's principal (主要的) dancer Misty Copeland.

    This was not a real letter. But Copeland says it is very similar to letters from her childhood. While many dancers start at the age of three. Copeland only began to study ballet in 1995 as a thirteen-year-old.

    People often told her that she was too old, or that she didn't have the perfect body type (She is only 157 cm tall). Her family moved a lot, and it was sometimes difficult for her to attend ballet classes. But Copeland loved dancing and did not want to give up. She stayed with her ballet teacher during the week and spent time with her family only at the weekend. This was a difficult life, but she worked hard and won her first national competition when she was fourteen years old. Copeland joined the American Ballet Theatre in 2000 and performed in many ballets over the next few years. In 2007, she became a solo (单独的) performer, and in 2015 she became its principal dancer.

    Copeland is now a dancer, author and Broadway performer. She also stars in the 2015 film A Ballerina's Tale. So what's next? According to Copeland, anything is possible: "My career (职业) really is just now beginning."