单选题Within the arid regions (in which) their culture developed, the Bedouin camel-breeding tribes have maintained a distinctive pattern and a dominant position (over) other societies and (settlements) (through) virtue of their ability to exploit brazing ranges.

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 ceils 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With a wave of his hand, the magician made the duck ______ A. scatter B. vanish C. abandon D. fly away

单选题If they think they are going to win over us by obstinately______and refusing to make the slightest concession, they are mistaken. A. holding out B. holding to C. holding over D. holding up

单选题John Smith is a______ ; he helps to write newspapers.

单选题One day in 1963, a dolphin named Elvar and a famous astronomer, Carl Sagan, were playing a little game. The astronomer was visiting an institute which was looking into the way dolphins communicate with each other. He was standing at the edge of one of the tanks where several of these highly intelligent, friendly creatures were kept. Elvar had just swum up alongside him and had turned on his back. He wanted Sagan to scratch his stomach again, as the astronomer had done twice before. But this time Elvar was too deep in the water for Sagan to reach him Elvar looked up at Sagan, waiting. Then, after a minute or so, the dolphin leapt up through the water into the air and made a sound just like the word "More!" The astonished astronomer went to the director of the institute and told him about the incident. "Oh, yes. That's one of the words he knows," the director said, showing no surprise at all. Dolphins have bigger brains in proportion to their body size than humans have, and it has been known for a long time that they can make a number of sounds. What is more, these sounds seem to have different functions, such as warning each other of danger. Sound travels much faster and much further in water than it does in air. That is why the parts of the brain that deal with sound are much better developed in dolphins than in humans. But can it be said that dolphins have a "language" in the real sense of the word? Scientists don't agree on this. A language is not just a collection of sounds, or even words. A language has a structure, or what we call a grammar. The grammar of a language helps to give it meaning. For example, the two questions "Who loves Mary?" and "Who does Mary love?" mean different things. If you stop to think about it, you will see that this difference doesn't come from the words in the question but from the difference in structure. That is why the question "Can dolphins speak?" can't be answered until we find out if dolphins not only make sounds but also arrange them in ways which affect their meaning.

单选题Building this road will ______ the construction of ten bridges, then the total cost reaches 1 million US Dollars. A. evolve B. involve C. revolve D. devolve

单选题It comes as no surprise that societies have codes of behavior. The character of the codes, on the other hand, can often be ______.

单选题Roger gave me some beautiful Japanese stamps in______ for two sets of 1960 British special issue.

单选题Most people______ driving on icy roads, but he rather enjoys it.

单选题Part of the lake has been polluted. You can see the water is covered with ______ oil.

单选题Even the most arbitrary and______ corporation today must be aware of the attitudes of its employees; management may at times be more or less______, but all must respect the power of an organized work force.

单选题The author believes that in the era of the Information Technology boom the distance between people' s hearts has become the farthest distance on earth because ______.

单选题There have been several attempts to introduce gayer colors and styles in men's clothing, but none of them ______.

单选题For us it is a big and dark secret;to______it would be to jeopardize our future, confessed an avi-aphobe who is currently undergoing therapy.

单选题Fossils of A(plant) that have B(been extinct) for C(fifty million years) have been found in large deposits of amber D(near) the Baltic Sea.

单选题The word "foolish" is too mild to describe your behavior. I would prefer the word ______.

单选题He studied at a famous college when he was young, ______contributed to his success in later life.

单选题The destruction of the Twin Towers in New York City ______ shock and anger throughout the world.