单选题It is believed that nomadic ancestors considered bumper harvests as bounty form the "God of Sun" and natural disasters as punishment.

单选题Passage Four Theoretical physicists use mathematics to describe certain aspects of Nature. Sir Isaac Newton was the first theoretical physicist, although in his own time his profession was called "natural philosophy". By Newton's era people had already used algebra and geometry to build marvelous works of architecture, including the great cathedrals of Europe, but algebra and geometry only describe things that are sitting still. In order to describe things that are moving or changing in some way, Newton invented calculus. The most puzzling and intriguing moving things visible to humans have always been the sun, the moon, the planets and the stars we can see in the night sky. Newton's new calculus, combined with his "Laws of Motion", made a mathematical model for the force of gravity that not only described the observed motions of planets and stars in the night sky, but also of swinging weights and flying cannonballs in England. Today's theoretical physicists are often working on the boundaries of known mathematics, sometimes inventing new mathematics as they need it, like Newton did with calculus. Newton was both a theorist and an experimentalist. He spent many long hours, to the point of neglecting his health, observing the way Nature behaved so that he might describe it better. The so-called "Newton's Laws of Motion" are not abstract laws that Nature is somehow forced to obey, but the observed behavior of Nature that is described in the language of mathematics. In Newton's time, theory and experiment went together. Today the functions of theory and observation are divided into two distinct communities in physics. Both experiments and theories are much more complex than back in Newton's time. Theorists are exploring areas of Nature in mathematics that technology so far does not allow us to observe in experiments. Many of the theoretical physicists who are alive today may not live to see how the real Nature compares with her mathematical description in their work. Today's theorists have to learn to live with ambiguity and uncertainty in their mission to describe Nature using math. In the 18th and 19th centuries, Newton's mathematical description of motion using calculus and his model for the gravitational force were extended very successfully to the emerging science and technology of electromagnetism. Calculus evolved into classical field theory. Once electromagnetic fields were thoroughly described using mathematics, many physicists felt that the field was finished, that there was nothing left to describe or explain. Then the electron was discovered, and particle physics was born. Through the mathematics of quantum mechanics and experimental observation, it was deduced that all known particles fell into one of two classes: bosons or fermions. Bosons are particles that transmit forces. Many bosons can occupy the same state at the same time. This is not true for fermions, only one fermion can occupy a given state at a given time, and this is why fermions are the particles that make up matter. This is why solids can't pass through one another, why we can't walk through walls—because of Pauli repulsion-the inability of fermions (matter) to share the same space the way bosons (forces) can. While particle physics was developing with quantum mechanics, increasing observational evidence indicated that light, as electromagnetic radiation, traveled at one fixed speed (in a vacuum) in every direction, according to every observer. This discovery and the mathematics that Einstein developed to describe it and model it in his Special Theory of Relativity, when combined with the later development of quantum mechanics, gave birth to the rich subject of relativistic quantum field theory. Relativistic quantum field theory is the foundation of our present theoretical ability to describe the behavior of the subatomic particles physicists have been observing and studying in the latter half of the 20th century. But Einstein then extended his Special Theory of Relativity to encompass Newton's theory of gravitation, and the result, Einstein's General Theory of Relativity, brought the mathematics called differential geometry into physics. General relativity has had many observational successes that proved its worth as a description of Nature, but two of the predictions of this theory have staggered the public and scientific imaginations: the expanding Universe, and black holes. Both have been observed, and both encapsulate issues that, at least in the mathematics, brush up against the very nature of reality and existence. Relativistic quantum field theory has worked very well to describe the observed behaviors and properties of elementary particles. But the theory itself only works well when gravity is so weak that it can be neglected. Particle theory only works when we pretend gravity doesn't exist. General relativity has yielded a wealth of insight into the Universe, the orbits of planets, the evolution of stars and galaxies, the Big Bang and recently observed black holes and gravitational lenses. However, the theory itself only works when we pretend that the Universe is purely classical and that quantum mechanics is not needed in our description of Nature. String theory is believed to close this gap. Originally, string theory was proposed as an explanation for the observed relationship between mass and spin for certain particles called hadrons, which include the proton and neutron. Things didn't work out, though, and Quantum Chromodynamics eventually proved a better theory for hadrons. But particles in string theory arise as excitations of the string, and included in the excitations of a string in string theory is a particle with zero mass and two units of spin. If there were a good quantum theory of gravity, then the particle that would carry the gravitational force would have zero mass and two units of spin. This has been known by theoretical physicists for a long time. This theorized particle is called the graviton. This led early string theorists to propose that string theory be applied not as a theory of hadronic particles, but as a theory of quantum gravity, the unfulfilled fantasy of theoretical physics in the particle and gravity communities for decades. But it wasn't enough that there be a graviton predicted by string theory. One can add a graviton to quantum field theory by hand, but the calculations that are supposed to describe Nature become useless. This is because, as illustrated in the diagram above, particle interactions occur at a single point of spacetime, at zero distance between the interacting panicles. For gravitons, the mathematics behaves so badly at zero distance that the answers just don't make sense. In string theory, the strings collide over a small but finite distance, and the answers do make sense. This doesn't mean that string theory is not without its deficiencies. But the zero distance behavior is such that we can combine quantum mechanics and gravity, and we can talk sensibly about a string excitation that carries the gravitational force. This was a very great hurdle that was overcome for late 20th century physics, which is why so many young people are willing to learn the grueling complex and abstract mathematics that is necessary to-study a quantum theory of interacting strings.

单选题Gene therapy and gene-based drugs are two ways we could benefit from our growing mastery of genetic science. But there will be others as well. Here is one of the remarkable therapies on the cutting edge of genetic research that could make their way into mainstream medicine in the coming years. While it"s true that just about every cell in the body has the instructions to make a complete human, most of those instructions are inactivated, and with good reason: the last thing you want for your brain cells is to start churning out stomach acid or your nose to turn into a kidney. The only time cells truly have the potential to turn into any and all body parts is very early in a pregnancy, when so-called stem cells haven"t begun to specialize. Yet this untapped potential could be a terrific boon to medicine. Most diseases involve the death of healthy cells—brain cells in Alzheimer"s, cardiac cells in heart disease, pancreatic cells in diabetes, to name a few; if doctors could isolate stem cells, then direct their growth, they might be able to furnish patients with healthy replacement tissue. It was incredibly difficult, but last fall scientists at the University of Wisconsin managed to isolate stem cells and get them to grow into neural, gut, muscle and bone cells. The process still can"t be controlled, and may have unforeseen limitations; but if efforts to understand and master stem cell development prove successful, doctors will have a therapeutic tool of incredible power. The same applies to cloning, which is really just the other side of the coin; true cloning, as first shown with the sheep Dolly two years ago, involves taking a developed cell and reactivating the genome within, resetting its developmental instructions to a pristine state. Once that happens, the rejuvenated cell can develop into a full fledged animal, genetically identical to its parent. For agriculture, in which purely physical characteristics like milk production in a cow or low fat in a hog have real market value, biological carbon copies could become routine within a few years. This past year scientists have done for mice and cows what Ian Wilmut did for Dolly, and other creatures are bound to join the cloned menagerie in the coming year. Human cloning, on the other hand, may be technically feasible but legally and emotionally more difficult. Still, one day it will happen. The ability to reset body cells to a pristine, undeveloped state could give doctors exactly the same advantages they would get from stem cells: the potential to make healthy body tissues of all sorts, and thus to cure disease. That could prove to be a true "miracle cure."

单选题The Asian tiger mom that Amy Chua portrays in her new book may seem like just one more species in the genus Extreme Parent — the counterpart to the hovering American Parents helicopters or the Scandinavian Curling Parents, who frantically rush ahead of their children, sweeping their paths clear of the tiniest obstacles. The common characteristics include an obsession with a child's success, a reflex to treat kids as extensions or reflections of oneself and patterns of conduct that impartial observers might class as insane if not criminal, if not both. In Chua's case, this famously includes prohibiting grades lower than an A, TV, playdates and sleepovers, and warning her pianist child that "if the next time's not PERFECT, I'm going to TAKE ALL YOUR STUFFED ANIMALS AND BURN THEM." In the case of the classic Western helicopter parent, it starts with Baby Einstein and reward charts for toilet training, and it never really ends, which is why colleges have to devote so many resources to teaching parents how to leave their kids alone. But it is the differences between the Tigers and the Choppers that help explain the furor Chua has caused, at least in the U. S. Tigers fixate on success, defined as achievement in precision-oriented fields like music and math; Choppers are obsessed with failure and preventing it at all costs. Tigers operate in a culture of discipline; Choppers, in a culture of fear. Tigers view children as tough, able to take the abuse; Choppers view them as precious, to be raised under glass. Their fury at a bad grade is more likely to land on the teacher than on the child. And if Chua appears to sentence her children to slave labor, Western parents enshrine their children and crave their friendship. "The thing that impresses me most about America," observed Edward, Duke of Windsor, who knew something about indulgence, "is the way parents obey their children." There is something bracing about Chua's apparent indifference to her daughters' hostility, especially for parents who have learned that even if you let your teenagers spend 50 hours a week on Facebook, they'll still find reasons to hate you. The reactions to Chua's book, Battle Hymn of the Tiger Mother, have ranged from praise for her honesty to scorn for her "extreme, rigid and authoritarian approach," as one critic put it. But in less hysterical precincts, she elicits a more conflicted response. First reaction: My God, she's crazy. Second reaction: Maybe she's right. I suspect one reason the book has touched such a nerve is a suspicion among the Choppers that an excessive fear of failure guarantees it — that if you don't let your kids get clobbered now and then by a tough teacher, they'll never have the resilience to thrive as adults in a competitive economy. Twenty-first century parenting already seemed like a gladiatorial contest, its battles fought in playgrounds , at book clubs and especially online, with the rise of parenting websites where parents — O. K. , mainly moms — claw and bite. You let your toddler have Froot Loops? You quit karate lessons? Western parents may exalt freedom and self-expression, but in many ZIP codes, parenting is a highly conformist activity, with protocols every bit as strict as Chua's. Commenters spank the moms who appear insufficiently committed to breast feeding. Some of Chua's critics sound just as smug when they declare that the Tigers' " inside-the-box thinking is why Bill Gates, Steve Jobs, Michael Dell and/or a cure for cancer will never come from China. " Too much discipline, they argue, makes for submissiveness and lack of imagination, because imagination by its nature is subversive; it colors outside the lines. Likewise, invention, the creation of something utterly new, violates the authority of the present and the tyranny of tradition.But this much derision, I suspect, reflects some doubts. Western families have no monopoly on happiness, and those of the helicopter variety at least do not exactly encourage wild individuality in their children. Trust your instincts, Dr. Spock advised back in 1946; but that involves a leap of faith that many modern parents find terrifying. Helicopter parents are great believers in expertise: read enough books, consult enough professionals, and you can crack the parenting code. Chua's daughters are, by all accounts, girls any parent would be proud of. But maybe the real appeal is her tone of certainty in discussing something so confounding as child rearing — as if it's a puzzle to be solved rather than a picture to be painted, and there's no way to know what it will look like until it's done.

单选题______of the seven continents were placed in the Pacific Ocean, there would still be room left for another continent the size of Asia.

单选题Overall, it is going to become much easier for people to communicate ______ the Net Communicating with others in real time will soon be the norm.

单选题Within decades, PAN-type research will transform the Internet into the Life Net, a comprehensive ______ environment for human habitation.

单选题She raised her face to the rain, to the dark sky, ______rather than frightened by this sudden wildness coming up from nothing around her.

单选题The American businessman had difficulty at times working with his local counterparts in Guangdong Province, for he could speak______Cantonese than Mandarin.

单选题Eye contact is important in relationship because it ______to show attention and interest.

单选题The nuclear family ______a self-contained, self-satisfying unit composed of father, mother and children.

单选题The two main causes are population pressures, especially the pressures (of) large metropolitan populations, and the desire—a (highly) commendable one—to bring a decent (life) at the lowest possible cost to the (largest) possible number of people.

单选题Since the price you quoted would leave us no margin of ______, we must do business with other suppliers who are offering lower prices for Dinner Sets of the same quality.

单选题In 1976 Sarah Caldwell became______at the Metropolitan Opera House in New York City.

单选题 In the 1960s, medical researchers Thomas Holmes and Richard Rahe developed a checklist of stressful events. They appreciated the tricky point that any major change can be stressful. Negative events like "serious illness of a family member" were high on the list, but so were some positive life-changing events, like marriage. When you take the Holmes-Rahe test you must remember that the score does not reflect how you deal with stress—it only shows how much you have to deal with. And we now know that the way you handle these events dramatically affects your chances of staying healthy. By the early 1970s, hundreds of similar studies had followed Holmes and Rahe. And millions of Americans who work and live under stress worried over the reports. Somehow, the research got boiled down to a memorable message. Women's magazines ran headlines like "Stress causes illness!" If you want to stay physically and mentally healthy, the articles said, avoid stressful events. But such simplistic advice is impossible to follow. Even if stressful events are dangerous, many—like the death of a loved one—are impossible to avoid. Moreover, any warning to avoid all stressful events is a prescription for staying away from opportunities as well as trouble. Since any change can be stressful, a person who wanted to be completely free of stress would never marry, have a child, take a new job or move. The notion that all stress makes you sick also ignores a lot of what we know about people. It assumes we're all vulnerable and passive in the face of adversity. But what about human initiative and creativity? Many come through periods of stress with more physical and mental vigor than they had before. We also know that a long time without change or challenge can lead to boredom, and physical and mental swain.

单选题On AIDS Day, the minister of Health Department demanded that the problems______paid special attention to.

单选题Being told I would be expected to talk here, I inquired what sort of a talk I ought to make. They said it should be something suitable to youth something didactic, instructive, or something in the nature of good advice. Very well, I have a few things in my mind which I have often longed to say for the instruction of the young; for it is in one"s tender early years that such things will best take root and be most enduring and most valuable. First, then, I will say to you, my young friends and I say it beseechingly—Always obey your parents, when they are present. This is the best policy in the long run, because if you don"t they will make you. Most parents think they know better than you do, and you can generally make more by humoring that superstition than you can by acting on your own better judgment. Be respectful to your superiors, if you have any, also to strangers, and sometimes to others. If a person offends you, and you are in doubt as to whether it was intentional or not, do not resort to extreme measures; simply watch your chance and hit him with a brick. That will be sufficient. If you shall find that he had not intended any offense, come out frankly and confess yourself in the wrong when you struck him; acknowledge it like a man and say you didn"t mean to. Yes, always avoid violence; in this age of charity and kindliness, the time has gone by for such things. Leave dynamite to the low and unrefined .

单选题More optimistic analysts argue that as the types of companies that provide dividends tend to have higher cash flows.

单选题The new______of knowledge has created ______people: everyone believes that his or her subject cannot and possibly should not be understood by others.

单选题The Chairman was evidently ______ by Jim's words and glared at him for a few seconds.