One day, Mr. Arnold was teaching a lesson, and things were going as normally as ever. He was explaining the story of human being to his pupils. He told them that, in the beginning, men were nomads (游牧); they never stayed in the same place for very long. Instead, they would travel about, here and there, in search of food, wherever it was to be found. And when the food ran out, they would move off somewhere else.

    He taught them about the invention of farming and keeping animals. This was an important discovery, because by learning to cultivate (耕作) the land, and care for animals, mankind would always have food steadily. It also meant that people could remain living in one place, and this made it easier to set about tasks that would take a long while to finish, like building towns, cities, and all that were in them. All the children were listening attracted by this story, until Lucy jumped up:

    “And if that was so important and improved everything so much, why are we nomads all over again, Mr. Arnold?”

    Mr. Arnold didn't know what to say. Lucy was a very clever girl. He knew that she lived with her parents in a house, so she must know that her family were not nomads; so what did she mean?

    “We have all become nomads again,” continued Lucy, “The other day, outside the city, they were cutting the forest down. A while ago a fisherman told me how they fish. It's the same with everyone: when there's no more forest left the foresters go elsewhere, and when the fish run out the fishermen move on. That's what the nomads did, isn't it?

    The teacher nodded, thoughtfully. Really, Lucy was right. Mankind had turned into nomads. Instead of looking after the land in a way that we could be sure it would keep supplying our needs, we kept developing it until the land was bare. And then off we would go to the next place! The class spent the rest of the afternoon talking about what they could do to show how to be more civilized (文明的).

    The next day everyone attended class wearing a green T-shirt, with a message that said “I am not a nomad!”

    And, from then on, they set about showing that indeed they were not. Every time they knew they needed something, they made sure that they would get it using care and control. If they needed wood or paper, they would make sure that they got the recycled kind. They ordered their fish from fish farms, making sure that the fish they received were not too young and too small. They only used animals that were well cared for, and brought up on farms.

    And so, from their little town, those children managed to give up being nomads again, just as prehistoric men had done, so many thousands of years ago.

阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。

    There are many useful suggestions that can help one to improve English. Here are some of them to increase one's English language vocabulary.

    Learning English vocabulary is about much more than just learning the right words. It is based on understanding important words and expressions.

    Learning a word will not help very much if you quickly forget it. Researches show that it takes from 10 to 20 repetitions(重复) to really make a word part of your vocabulary. Since most words are learned from how they are used in context (上下文), the more words one is shown, the better vocabulary one will have. Keep a piece of paper close to you. When you read, pay close attention to the word you do not know, write the word down and try to understand its meaning from the context. Then look up the word in a dictionary. 

    Remember that if you do not use English words that you have just learned in conversation or writing, you will forget them very quickly. So the best way to learn new words effectively is just by trying to use them in conversation and writing. Remember also that practice is the key to fluent spoken English.

    Building vocabulary is a life-long task. Remember: ＂In the beginning was the word.＂ Your future could depend on how rich your vocabulary is. It will also determine the quality of your communication.

A

    In no particular order, here are some songs on the Music app of my phone:

On a Sunday Afternoon by Lighter Shade of Brown— A student of mine introduced this rap song to me all the way back in the early 1990s, when I was teaching Spanish at a local university. The story in the song takes place not too far from where I live in Los Angeles. It's a good "driving" song, nothing difficult or "deep".

Say Something by A Great Big World—A more recent song about a couple losing contact with each other. The piano part is of very little playing but beautiful.

    The Weight by The Band — Another old song, originally made public in 1968, but one I didn't hear until I was in high school more than 10 years later. I don't understand the words to the song completely, but the feeling of the song is very comforting to me.

Under the Bridge by Red Hot Chili Peppers — This Los Angeles group wrote a song that I used to listen to when I first moved to LA more than 25 years ago. I didn't know anyone here when I first arrived. When I got bored, I used to drive up and down the major streets that cross the city from east to west, listening to this song about t4the city of angels" being as "lonely as I am" (Don't worry. I have plenty of friends now.)

    There is some unwelcome news for students preparing for exams and officers putting in long hours—you don't need that "refreshment（提神） break" as much as you may think.

    Scientists believed it was not easy for people to continue their work if they felt the need to have a snack or a rest to make them feel better. They argued that the only way to regain willpower is by supplying more energy to our bodies with rest, food or entertainment.

    But psychologists have challenged this theory, saying weak willpower is in your head. They found that a person's mindset(理念) and belief about willpower determine how long and how well they'll be able to work on a tough mental exercise. "If you think of willpower as something that's limited, you're more likely to be tired when you perform a difficult task," said Professor Veronika Job. "But if you think of willpower as something that is not easily depleted, you can go on and on."

    The researchers led by Mr. Job designed an experiment to test the students' beliefs about willpower. After a tiring task those who believed or were led to believe that willpower was a limited resource performed worse on standard concentration tests than those who thought of willpower as something they had more control over.

    Mr. Job said, "Students who may already have trouble studying are being told that their powers of concentration are limited, and they need to take frequent breaks. But a belief in willpower as a non-limited resource makes people stronger in their ability to work through challenges."

    The findings could help people who are battling with temptation(诱惑): people following strict diets and doing exercise regularly to lose weight, people trying to overcome addictions, employees facing a tight deadline. Willpower isn't driven by a biologically based process as much as we used to think.

    You can't always predict a heavy rain or remember your umbrella. But designer Mikhail Belvacv doesn't think that forgetting to check the weather forecast before heading out should result in you getting wet.

    That's why he created Lampbrella, a lamp post with its own rain sensing umbrella.

    The designer says he came up with the idea after watching people get wet on streets in Russia. "Once, I was driving on a central Saint Petersburg street and saw the street lamps lighting up people trying to hide from the rain. I thought it would be appropriate to have a canopy(伞蓬) built into a street lamp," he said.

    The Lampbrella is a standard-looking street lamp fitted with an umbrella canopy. It has a built-in electric motor which can open or close the umbrella on demand. Sensors (传感器)then ensure that the umbrella offers pedestrians shelter whenever it starts raining.

    In addition to the rain sensor, there's also a 360 motion sensor on the fiberglass street lamp which detects whether anyone's using the Lampbrella. After three minutes of not being used the canopy is closed.

    According to the designer, the Lampbrella would move at a relatively low speed, so as not to cause harm to the pedestrians. Besides, it would be grounded to protect from possible lighting strike. Each Lampbrella would offer enough shelter for several people. Being installed at 2 meters off the ground it would only be a danger for the tallest of pedestrians.

    While there are no plans to take Lampbrella into production, Belyaev says he recently introduced his creation to one Moscow Department and insists this creation should be installed on the street where a lot of people walk but there are no canopies to provide shelter.

    Is there a way to turn back the aging process in people? For centuries, people have been looking for a "fountain of youth." The idea is that if you find a magical fountain, and drink its water, you will not age.

    Researchers in New York did not find an actual fountain of youth, but they may have found a way to turn back the aging process. It appears that the answer may be called the hypothalamus, which is part of your brain. It controls important body activities, including growth, the way we process food and so on. Researchers found that hypothalamus neural stem cells (干细胞) also influence how fast aging takes place.

    Dongsheng Cai was the leading researcher in a study on aging in mice. He and his team reported their findings. "when the hypothalamus starts aging, particularly the loss of hypothalamus stem cells, so does the body." he said.

    Using this information, the researchers began trying to activate (激活) the hypothalamus in laboratory mice. The results show that the treatment slowed aging in the animals. "When we injected the hypothalamus stem cells to the middle-aged mice, the mice aged slowly and they could also live longer."

    But these results were just from studying mice in a laboratory. If the mice can live longer, does that mean people could have longer lives? The next step is to see if the anti-aging effects also work in human beings. If so, they say the findings could lead to new ways to help doctors identify and treat age-related health problems.