How does an ecosystem(生态系统)work？What makes the populations of different species the way they are？Why are there so many flies and so few wolves？To find an answer，scientists have built mathematical models of food webs，noting who eats whom and how much each one eats.
With such models，scientists have found out some key principles operating in food webs. Most food webs，for instance，consist of many weak links rather than a few strong ones. When a predator(掠食动物)always eats huge numbers of a single prey(猎物)，the two species are strongly linked；when a predator lives on various species，they are weakly linked. Food webs may be dominated by many weak links because that arrangement is more stable over the long term. If a predator can eat several species，it can survive the extinction(灭绝)of one of them. And if a predator can move on to another species that is easier to find when a prey species becomes rare，the switch allows the original prey to recover. The weak links may thus keep species from driving one another to extinction.
Mathematical models have also revealed that food webs may be unstable，where small changes of top predators can lead to big effects throughout entire ecosystems. In the 1960s，scientists proposed that predators at the top of a food web had a surprising amount of control over the size of populations of other species---including species they did not directly attack.
And unplanned human activities have proved the idea of top-down control by top predators to be true. In the ocean，we fished for top predators such as cod on an industrial scale，while on land，we killed off large predators such as wolves. These actions have greatly affected the ecological balance.
Scientists have built an early-warning system based on mathematical models. Ideally，the system would tell us when to adapt human activities that are pushing an ecosystem toward a breakdown or would even allow us to pull an ecosystem back from the borderline. Prevention is key，which scientists says because once ecosystems pass their tipping point(临界点)，it is remarkably difficult for them to return.
1.What have scientists discovered with the help of mathematical models of food webs？
A.The living habits of species in food webs.
B.The rules governing food webs of the ecosystems.
C.The approaches to studying the species in the ecosystems.
D.The differences between weak and strong links in food webs.
2.A strong link is found between two species when a predator______
A.has a wide food choice B.can easily find new prey
C.sticks to one prey species D.can quickly move to another place
3.What conclusion can be drawn from the examples in Paragraph 4？
A.Uncontrolled human activities greatly upset ecosystems.
B.Rapid economic development threatens animal habitats.
C.Species of commercial value dominate other species.
D.Industrial activities help keep food webs stable.
4.How does an early-warning system help us maintain the ecological balance？
A.By getting illegal practices under control.
B.By stopping us from killing large predators.
C.By bringing the broken-down ecosystems back to normal.
D.By signaling the urgent need for taking preventive action.
You can’t walk into the office without Rihanna’s voice singing “work work work work work work” in your head. And that one line from Lady Gaga’s “Bad Romance” still makes you want to scream. These are commonly known as earworm songs—those sticky tunes that continue to play in your head. A recent study finds that more than 90% of adults report hearing earworm songs on a weekly basis.
Fortunately, most people report earworm songs as pleasant. But others find them annoying or even maddening. “Some people are troubled by them to the point that it disturbs life,” says Elizabeth Hellmuth Margulis, a professor at the University of Arkansas who has studied earworm songs.
Margulis says earworm songs tend to have some predictable characteristics. For one thing, they tend to small parts of a song—not the whole track. And “the songs you’ve heard recently also have the most possibility to get stuck in your memory,” she says.
But sometimes something strange and unpredictable can also start a track paying in your head. “Once I was at the doctor’s office and saw a poster of a man who I thought looked like Gaston—a character from Beauty and the Beast,” Margulis recalls. A couple minutes passed, and she realized she couldn’t get “Be Our Guest”, the song in the movie, out of her head, even though she hadn’t thought of the tune in years. In that instance, she was able to identify her earworm’s trigger: the Gaston-looking man in the poster. “But the connections can be really unclear,” she says.
Margulis points out that, in all of human history, recorded music is a very new phenomenon. She says some have inferred that earworm songs are also new—the unintended consequence of being able to hear the same song played everywhere in the same way over and over again. So far, the convincing explanation for why human beings experience earworm songs remains a mystery. But there are some well-established ways to cast off the earworm songs.
“Finding a mentally demanding task and putting your mind on it usually shifts attention away from internal music. People tend to get earworms when performing tasks that don’t require their full attention—stuff like doing the dishes,” Margulis says.
Chewing gum can also help. When a song is stuck in our heads, it’s almost like we’re singing along with it. If you make your mouth do something else—chewing gum, eating a meal or talking with a friend—that can kick out the earworm.
You could also face your enemy. By listening to the full track that includes the passage stuck in your head, you may find “closure” and relief.
1.Which of the following is most likely to be an earworm song?
A.A song made up of simple words.
B.A song heard frequently these days.
C.A song sung by a most famous singer.
D.A song learned during one’s childhood.
2.What does the underlined word “trigger” in Paragraph 4 mean?
A.Type. B.Tune.
C.Cause. D.Characteristic.
3.We can infer that earworm songs may ________.
A.result from modern technology B.be experienced over meals
C.help regain lost memories D.hurt one’s hearing
4.What is mainly talked about in the last three paragraphs?
A.Why we hear earworm songs. B.Where to find earworm songs.
C.When we hear earworm songs. D.How to get over earworm songs.
I once heard this tale in India, where it is told as if true—though any naturalist would know it couldn’t be. The country is India. A colonial official and his wife are giving a large dinner party. They invite army officers and their wives, and a visiting American naturalist.
A spirited discussion springs up between a young girl who says women are no longer the jumping on a chair at the sight of a mouse and an army officer who disagrees and says, “A woman’s reaction in any crisis is to scream. And a man has more control than a woman.”
The American scientist does not join in the argument but sits and watches the faces of the other guests. As he stares, he sees a slight strange expression come over the face of the hostess. She gestures to the servant standing behind her chair and whispers to him. The servant’s eyes widen. He turns quickly and leaves the room. Of the guests, none except the American notices this or sees the servant place a bowl of milk on the balcony just outside the open glass doors.
In India, milk in a bowl means only one thing: bait (诱饵) for a snake. The American understands there must be a snake in the room. His eyes move across the room but see nothing. He realizes the snake can only be in one place — under the table.
His first reaction is to jump back and warn the others. But he knows any sudden movement will frighten the animal into striking. He speaks quickly, the tone of his voice so arresting that it quietens everyone. “I want to know what control everyone here has. I will count three hundred—that’s five minutes — and not one of you is to move a muscle. Ready!”
The 20 people sit like stone images while he counts. He is saying, “—two hundred and eighty—” When out of the corner of his eyes, he sees the snake make for the bowl of milk. Four or five screams ring out as he jumps to close the balcony doors.
“There is your proof!” the host shouts. “A man has just shown us perfect self-control.”
“Just a minute,” the American says, turning to his hostess, “How did you know that snake was in the room?” With a faint smile coming across her face she replies: “Because it was lying across my foot.”
1.What can we conclude from the passage?
A.Women are afraid of mice.
B.The army officer’s opinion is wrong.
C.The American suggests playing a game for entertainment.
D.The hostess has had previous experience catching snakes.
2.Choose the right order of the events given in the passage.
a. The American’s eyes sweep the room but he sees nothing.
b. The American suggests the guests playing a game.
c. Following the instructions, the servant puts out some milk.
d. The hostess is staring ahead, a slight strange look appearing.
e. The American shuts the balcony doors safely, and several screams are let out.
f. The snake edges its way to the bowl of milk.
A.d,c,a,b,f,e B.a,b,c,e,f,d
C.d,f,a,b,c,c D.f,e,c,a,d,b
3.Who has real self-control according to the passage?
A.The American. B.The army officer.
C.The girl. D.The hostess.
4.What may be the best title for the passage?
A.A Heated Argument B.A Striking Dinner Party
C.An Unbelievable Story D.A Smart Hostess
Kids Flying Alone Guide
Helpful tips for children traveling alone | |||
Airline | Age | Fee per child (each way). | Notes |
Air Tran Airways | 6 to 8 years old — non-stop or direct flights only | $ 48 for a non-stop flight | Unaccompanied children. |
American | 6 to 8 years old — non-stop or direct flights only | $ 110 | Flights for unaccompanied children cannot be booked online. |
British Airways | 7 to 15 years old — can travel alone on connecting flights | $ 60 for flights within UK | Flights for unaccompanied children cannot be booked online. |
Frontier Airlines | 6 to 15 years old — non-stop or direct flights or connecting flights | $ 60 for non-stop or direct flights $120 for connecting flights | Flights for unaccompanied children cannot be booked online. |
Before the flight:
Try to book a morning flight. If it is delayed or canceled, you have the rest of the day to make alternate planes. Make sure your child doesn’t wear any clothing that has his or her name on it, which would make it easier for a stranger to convince a child he can be trusted.
At the airport:
Make sure the flight attendants know that your child is traveling alone. Make sure that he or she will be seated in an area of the aircraft that’s convenient for attendants to keep an eye on — the very front of very back of the aircraft is ideal.
Register your child’s travel plans with the U. S. State Department, which can provide assistance in an emergency. This is a free service.
What to pack:
Cell phone: If your child doesn’t have a cell phone, buy him or her a pay-as-you-go phone at a cell phone retailer (零售店) so he or she has an easy form of communication for emergencies.
Gift cards: Invest in a few pre-paid gift cards worth $ 25 or $ 50, This will reduce the worry of traveling with a large amount of cash.
Family/ friends contact information: Give your child a complete list of names, numbers and addresses of the people who are picking your child up at the airport.
1.How much should you pay if your child aged eleven travels alone on a connecting flight by Frontier Airlines?
A.$ 50. B.$ 75.
C.$ 120. D.$ 160.
2.What can we learn from the passage?
A.Juice or water can’t be brought onto the aircraft.
B.Unaccompanied children can’t fly on the last flight of the day.
C.Pay-as-you-go phones are provided for free at the airport for children without cell phones.
D.Parents can register children’s travel plans with the U. S. State Department for free.
3.Which of the following is recommended for unaccompanied children?
A.Booking them morning flights.
B.Giving them a large amount of cash.
C.Making them sit in the middle of the aircraft.
D.Dressing them in clothing with their names on it.
假设你叫李华，是一家英文杂志社的心理咨询师。某中学生小王给你写信，提到自己偏胖，想节食减肥，征求你的意见。请你给她回一封信，谈谈你对该问题的见解。内容要点如下：
1．健康比漂亮更重要；
2．学生以学习为主，不要过于注重外貌和别人的看法；
3．可通过多锻炼身体保持健康，要改变不良的饮食习惯；
4．健康的心态也很重要。
注意： 1．短文必须包括所有内容要点，可适当发挥；
2．词数：100左右。 3．参考词汇：state of mind 心态
Dear Xiao Wang,
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
Yours
下面短文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。
增加：在缺词处加一个漏字符号(∧), 并在其下面写出该加的词。
删除：把多余的词用斜线（﹨）划掉。
修改：在错的词下面划一横线，并在该词下面写出改正后的词。
注意：1. 每处错误及其修改均仅限一词;
2. 只允许修改10处，多者（从第11处起）不计分。
My family took an amazed trip to the northwest last summer. At the first ,we flew to Lanzhou but then visited the famous Iron Bridge there.We also tasted Lanzhou beef noodles, which were the most delicious noodles I had never had. Two days late， we went to the Mogao caves on the Silk Road. That impressed me most was the fantastic wall paintings. Finally，we reach our final destination，the Qinghai Lake，surrounded by mountains. The scenery was unbelievable beautiful. We found volunteers collecting rubbishes along the bank and we joined them too. Only then I realize we could make a difference to our environment.
