单选题They agreed to modify their policy.

单选题Volunteers are being recruited(征募) to eat raw potatoes in the first human trials of a vaccine grown in genetically engineered vegetables. Researchers in Texas hope that people who eat the potatoes will be protected against common gut(肠，肠子) infections. They believe this technique could prove to be a cost-effective way of growing vaccines in developing countries where such diseases are still killers. Other researchers previously succeeded in using similar techniques to produce potential vaccines Now Hugh Mason and his colleagues at Texas A & M University(得克萨斯农业及机械大学) their plant vaccines on mice and plan to recruit 15 volunteers for a human trial. The team first tested the technique in tobacco plants. They took a strain of Escherichia coli(大肠杆菌) bacteria that causes food poisoning, and identified the part of the poison which binds to its victims gut cells. They then used a modified plant bacterium called Agrobacterium tumefasciens to transfer the segment of DNA which manufactures the binding protein into the tobacco plant. Under normal circumstances, these bacteria transfer packets of DNA into plant cells to force the plant to manufacture the nutrients they need. But in the modified bacteria, the DNA package includes the gene to pro- duce the binding protein. Once the foreign DNA segment was incorporated(结合，合并) into the tobacco's own DNA, the bacteria were killed off with antibiotics. Mason's team then grew these modified tobacco plants and found that they produced the E. coli binding protein. Proof of success came when the tobacco leaves were mashed up(捣碎) and squirted into the stomachs of mice. Mason says that within days the mice started producing specific antibodies to the E. coli poison, but suffered no ill effects from digesting the binding protein. Mason then produced genetically engineered potatoes and fed these to mice, with similar results. Mason's team have used plants to produce vaccines against a number of other infectious agents. For example, they have made a vaccine using a protein from the shell of the Norwalk virus, which causes diarrhoea(腹泻) in children. A third vaccine has also been produced in tobacco using a surface protein from the hepatitis B virus. But Mason says that so far they have only been able to produce small amounts of it in potatoes. Although a vaccine already exists against hepatitis B, a cheaper plant version could make mass immunisation(群众性免疫) possible. One problem with growing potatoes to produce vaccines is that cooking tends to destroy the protein component of the vaccine, so they must be eaten raw. Mason thinks that bananas may be a better option. "One banana could potentially produce a whole host of different vaccines," says Mason.

单选题 阅读下面的短文，文中有15处空白，每处空白给出了4个选项，请根据短文的内容从 4个选项中选择1个最佳答案。 {{B}}A Special Clock{{/B}} Every living thing has what scientists call a biological clock that controls behavior. The biologicai clock______(51) plants when to form flowers and when the flowers should open. It tells insects when to______(52) the protective cocoon (防护卵袋) and fly away, and it tells animals and human beings when to eat, sleep and wake. Events outside the plant and animal______(53) the actions of some biological clocks. Scientists recently found, for example, that a tiny animal changes the color of its fur because of the______(54) of hours of daylight. In the short______(55) of winter, its fur becomes white. The fur becomes gray brown in______(56) in the longer hours of daylight in summer. Inner signals control other______(57) clocks. German scientists found that some kind of internal clock seems' to order birds to begin their long migration ______(58) twice each year. Birds______(59) from flying become restless when it is time for the trip,______(60) they become calm again when the time of the flight has ended. Scientists say they are beginning to learn which______(61) of the brain contain biological clocks. An American researcher, Martin Moorhead, said a small group of cells near the front of the brain______(62) to control the timing of some of our actions. These______(63) tell a person when to wake, when to______(64) and when to seek food. Scientists say there probably are other biological clock Cells that ______(65) other body activities.

单选题She is a lovely and gracious woman.

单选题At the age of 30, Hersey suddenly became a celebrity .

单选题Use of Trademarks A company must determine whether or not to apply for trademark protection under the federal Lanham Act of 1946 or state law. A trademark gives a firm exclusive use of a "word, symbol, combination of letters or numbers, or other devices such as distinctive packaging used to identify the goods of one company and to distinguish them from other companies" for as long as they are marketed. Trademarks are voluntary and require a registration procedure that can be time consuming, complex, and expensive. A multinational firm must register trademarks in every country in which it operates. In order for a trademark to be legally protected, it must have a distinctive meaning that does not describe an entire product category, not be confusingly similar to other trademarks, be used in interstate commerce, and not imply characteristics that the product does not possess. A surname by itself cannot be registered, because anyone can do business under his or her name. However, an surname can be registered if used to describe a specific business (e. g. ,Roy Roger's Restaurants). When brands become too popular or descriptive of a product category, they run the risk of becoming public property. Then a firm loses its trademark position. Brands that are fighting to remain exclusive trademarks include Xerox, Levi's Frigidaire, Formica, Kleenex, and Teflon. Brands of former trademarks that are now considered generic and therefore public property are cellophane(赛璐玢),aspirin, kerosene(煤油),cola, linoleum(漆布),and monopoly. DuPont used careful research to retain a trademark for Teflon. As company survey showed that 68 percent of the consumers questioned identified Teflon as a brand name. This enabled DuPont to win a court case against a Japanese firm using the name Teflon. On the other hand, the U. S. Supreme Court ruled that "Monopoly'was a generic term that could be used by any game maker. Likewise, a federal court ruled that Miller could not trademark the single word Lite for its lower-calorie(低热量) beer. Trademark protection is essential to many firms because exclusive use of brands and symbols enables them to maintain long-established images and market shares.

单选题The newspaper did not mention the degree of the damage caused by the fire.

单选题Because {{U}}administering{{/U}} the whole company, he sometimes has to work around the clock. A.adjusting B.evaluating C.engaging D.managing

单选题The travelers were ready to enjoy the spectacular tidal waves when suddenly a thick fog came up and obscured the whole scene. A. blurred B. belittled C. banned D. collapsed

单选题The researchers have just completed a study of driving situations.

单选题Techniques to (employ) the energy of the sun are being developed.

单选题We have to put up with her behavior.

单选题It is no use debating the relative merits of this policy.

单选题We cannot permit such {{U}}conduct{{/U}}. A. movement B. word C. principle D. behavior

单选题The great change of the city astonished all the visitors

单选题Our lives are intimately bound up with theirs. A. tensely B. nearly C. closely D. carefully

单选题The best country music songs are those that express an emotion that is likely to make a listener weep.A. smileB. thinkC. singD. cry

单选题I Urarely/U play basketball.

单选题The farmers worried about the {{U}}lack{{/U}} of rain.

单选题Even in a highly modernized country, Manual work is a still needed.