单选题 Valvular heart diseases are quite common, essentially resulting in impaired blood flow and were very difficult to treat. Some 30 years ago, it became possible to replace .diseased valves with prostheses to impose a greater control over blood flow. Early devices were of the mechanical variety, in which devices like ball-in-a-cage or tilting disc would be used to allow blood to flow under near-normal conditions. Although a few mechanical problems were encountered in the early days, the major difficulty lay with the tendency for any foreign material to initiate a blood clot. So, all valve recipients have to be given anticoagulant therapy. This is not particularly desirable for the patients, who may develop bleeding problems, and in any case is not always successful. Although good results are achieved with these valves, it was considered necessary to develop alternatives and the direction was that of natural tissues. It's not possible to transplant heart valves untreated because of rejection phenomena, but it became apparent that collagenous tissue could be cross-linked by glutaraldehyde and prepared in the form of a heart valve. Two sources of tissue were considered for this purpose, bovine pericardium ( collagenous tissue derived from the wall of a cow's heart) and porcine valves (heart valves taken from pigs) and the resulting "bioprosthetic valve" appeared to be very promising. It was particularly important that these patients didn't need anticoagulation. Unfortunately, these valves have not proved very durable, the cross-linked collagen suffering from slow calcification and deterioration so most of the replacement valves themselves need to be replaced within a decade. This would tend to suggest that the mechanical valves give superior performance, notwithstanding the anticoagulation problem, and a move back towards their use might have been expected. However, most of the valves in current use incorporate an alloy'( usually Stellite) forthe housing, and a carbon coated occuluder. The complex shapes of some of the housing have required combinations of casting and welding technologies to be used in their construction and serious problems have arisen with a valve design from one manufacturer, where a small number of catastrophic fractures have occurred within the housing. In patients where this valve has been used to treat aortic valve disease, this fracture is usually fatal and although the risks are small, the problem is important to the industry. Also, at a time when this dichotomy is exercising the minds of surgeons, scientists and regulatory bodies alike, the emergence of the disease BSE in cattle has placed even further restrictions on the use of animal tissue for this type of application and the whole question of prosthetic heart valves has been turned from a reasonable successful example of reconstructive implant surgery to a very confused area. This serves to highlight some of the very varied problems of facing the use of biomaterials.

单选题Many well-educated people don't believe that ______ will endanger freedom of speech.

单选题The book contained a large ______ of information.

单选题Her sadness was obvious, but she believed that her feeling of depression was______. (2004年清华大学考博试题)

单选题Henry viewed Melissa as ______; she seemed to be against any position regardless of its merits. A. heretical B. disobedient C. contrary D. inattentive

单选题You must always be ready to sacrifice ______ to duty. A. inclination B. tendency C. interest D. career

单选题One difficulty is that while other disciplines investigate a specific range of phenomena, philosophy, particularly in the hodgepodge conception, investigates all of existence.

单选题Forget what Virginia Woolf said about what a writer needs--a room of one's own. The writer she has in mind wasn't at work on a novel in cyberspaee, one with multiple hypertexts, animated graphics and downloads of trance, charming music. For that you also need graphic interfaces, Real Player and maybe even a computer laboratory at Brown University. That was where Mark Amerika--his legally adopted name; don't ask him about his birth name--composed much of his novel Gramatron. But Grammatron isn't just a story. It's an online narrative (gramatron. com) that uses the capabilities of cyberspace to tie the conventional story line into complicated knots. In the four years it took to produce-it was completed in 1997-each new advance in computer software became another potential story device. "I became sort of dependent on the industry," jokes Amerika, who is also the author of two novels printed on paper. "That's unusual for a writer, because if you just write on paper the 'technology' is pretty stable." Nothing about Gramatron is stable. At its center, if there is one, is Abe Golam, the inventor of nanograph a quasi mystical computer code that some unmystical corporations are itching to acquire. For much of the story, Abe wanders through Prague-23, a virtual "city" in cyberspace where visitors indulge in fantasy encounters and virtual sex, which can get fairly graphic. The reader wanders too, because most of Gramatron's 1,000-plus text screens contain several passages in hypertext. To reach the next screen just double-click. But each of those hypertexts is a trapdoor that can plunge you down a different pathway of the story. Choose one and you drop into a corporate-strategy memo. Choose another and there's a XXX-rated sexual rant. The st0ry you read is in some sense file story you make. Amerika teaches digital art at the University of Colorado, where his students develop works that straddle the lines between art, film and literature. "I tell them not to get caught up in mere plot," he says. Some avant-garde writers--Julio Cortazar, Italo Calvino-have also experimented with novels that wander out of their author's control. "But what makes the Net so exciting," says Amerika, "is that you can add sound, randomly generated links, 3-D modeling, animation." That room of one's own is turning into a fun house.

单选题Eventually the old brutal arrangement was______by the laws of the state, which undertook to end the freelance savageries of personal revenge by meting out justice uncomplicated by private passion.

单选题These advisors ______.

单选题Monochronic time (M-time) and polychronic time (P-time) represent two variant solutions to the use of both time and space as organizing frames for activities. Space is included because the two systems (time and space) are functionally interrelated. M-time emphasizes schedules, segmentation, and promptness. P-time systems are characterized by several things happening at once. They stress involvement of people and completion of transactions rather than adherence to preset schedules. P-time is treated as much less tangible than M-time. P-time is apt to be considered a point rather than a ribbon or a road, and that point is sacred. Americans overseas are psychologically stressed in many ways when confronted by P-time systems such as those in Latin America and the Middle East. In the markets and stores of Mediterranean countries, one is surrounded by other customers vying for the attention of a clerk. There is no order as to who is served next, and to the northern European or American, confusion and clamor abound. In a different context, the same patterns apply within the governmental bureaucracies of Mediterranean countries: A cabinet officer, for instance, may have a large reception area outside his private office. There are almost always small groups waiting in this area, and these groups are visited by government officials, who move around the room conferring with each. Much of their business is transacted in public instead of having a series of private meetings in an inner office. Particularly distressing to Americans is the way in which appointments are handled by polychronic people. Appointments just don't carry the same weight as they do in the United States. Things are constantly shifted around. Nothing seems solid or firm, particularly plans for the future, and there are always changes in the most important plans right up to the very last minute. In contrast, within the Western world, man finds little in life that is exempt from the iron hand of M-time. In fact, his social and business life, even his sex life are apt to be completely time dominated.

单选题The tendency of the human body to reject foreign matter is the main obstacle to successful organ transplantation.

单选题Living constantly in the atmosphere of slave, he became infected ______ the unconscious ______ their psychology. No one can shield himself ______ such an influence.

单选题As a salesman, he works on a______ basis, taking 10% of everything lie sells.

单选题Recent reform efforts (have been focused) on encouraging lifelong or recurrent education to meet (changing individual and social need). Thus, not only (the number of students has increased), (but) the scope of education has also expanded

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单选题Marriage therapists teach a skill called active listening. Each partner takes a turn listening then interprets what he/she has heard and validates(证实)it. There is, however, a problem. It rarely works. For 80 percent of couples, active listening is too hard. Even happy couples have screaming matches. Every time you raise a hot-button issue, such as — the in-laws or money, does your husband suddenly clam up？ More than 80 percent of the time, it is the wife who brings up tricky marital issues, while the husband tries to avoid discussing them. This isn't a symptom of a troubled marriage — it's true in most happy marriages. You'll often hear that staying in a bad marriage is worse, for everybody concerned — especially the children — than getting divorced. That may be true if your home is so full of hostility that it's like a war zone. But sociologist Linder J. Waite says she has found that 75 percent of couples who rated their marriages as miserable but stayed married were happy five years later. We usually think the strongest marriages are those that survive major traumas, such as bankruptcy or an extramarital affair. But frequently, dealing with the little things, those daily annoyances, eats away at a marriage. "Every couple experiences disappointment as initial romance and passion fade and they discover all their difference," says Wolin. "He doesn't do enough housework. She is too emotional. He watches too much TV. She's too lenient(宽容)with the kids. People think of these differences as problems, but they're actually opportunities to build marital muscles.

单选题Did he really expect her to smile now and______with his plans, treat all this deception as no more than an unusual diversion? A. fall in B. put off C. agree to D. stand up