单选题We resolved the problem after group discussion. A. caused B. met C. solved D. posed

单选题The study has posed a question about this nature.A. supportedB. cancelledC. arousedD. raised

单选题Nothing would {{U}}induce{{/U}} me to vote for him again. A. teach B. help C. attract D. discourage

单选题She was {{U}}grateful{{/U}} to him for being so good to her.

单选题The boy always looks through his homework before handing it in.

单选题It is postulated that a cure for the disease will have been found by the year 2020.

单选题 New Understanding of Natural Silk's Mysteries Natural silk, as we all know, has a strength that manmade materials have long struggled to match. In a discovery that sounds more like an ancient Chinese proverb than a materials science breakthrough, MIT researchers have discovered that silk gets its strength from its weakness. Or, more specifically, its many weaknesses. Silk gets its extraordinary durability and ductility from an unusual arrangement of hydrogen bonds that are inherently very weak but that work together to create a strong, flexible" structure. Most materials—especially the ones we engineer for strength—get their toughness from brittleness. As such, natural silks like those produced by spiders have long fascinated both biologists and engineers because of their light weight, ductility and high strength (pound for pound, silk is stronger than steel and far less brittle). But on its face, it doesn't seem that silks should be as strong as they are; molecularly, they are held together by hydrogen bonds, which are far weaker than the covalent bonds found in other molecules. To get a better understanding of how silk manages to produce such strength through such weak bonds, the MIT team created a set of computer models that allowed them to observe the way silk behaves at the atomic level. They found that the arrangement of the tiny silk nanocrystals is such that the hydrogen bonds are able to work cooperatively, reinforcing one another against external forces and failing slowly when they do fail, so as not so allow a sudden fracture to spread across a silk structure. The result is natural silks that can stretch and bend while retaining a high degree of strength. But while that's all well and good for spiders, bees and the like, this understanding of silk geometry could lead to new materials that are stronger and more ductile than those we can currently manufacture. Our best and strongest materials are generally expensive and difficult to produce (requiring high temperature treatments or energy-intensive processes). By looking to silk as a model, researchers could potentially devise new manufacturing methods that rely on inexpensive materials and weak bonds to create less rigid, more forgiving materials that are nonetheless stronger than anything currently on offer. And if you thought you were going to get out of this materials science story without hearing about carbon n anotubes, think again. The MIT team is already in the lab looking into ways of synthesizing silk-like structures out of materials that are stronger than natural silk—like carbon nanotubes. Super-silks are on the horizon.

单选题It's just a petty mistake. A. major B. important C. serious D. minor

单选题How many mobile phone users will there be in Australia by the year 2000, according to the passage?

单选题It is Uobvious/U that he will win the game,

单选题Not everyone can perceive the gradual change in the writer's style.A. appreciateB. noticeC. describeD. discover

单选题Some insects rely on the tiny hairs scattered over their bodies to sense sound waves.A. amplifyB. disguiseC. sendD. detect

单选题The governor gave a rather vague outline of his tax plan.

单选题They agreed to settle the dispute by peaceful means.

单选题Many people in the region have died from the epidemic disease. A. infectious B. inferior C. infinite D. inevitable

单选题They bought the land in order to build a new office block.

单选题We all think the prices of the computers will soon plunge .

单选题Computers in Cars You"re far from home on a lonely road. Shadowy forests stretch away on both sides. A thick mist (雾) makes it difficult to see far beyond your car"s windshield (挡风玻璃). "Can this be route 90A?" you wonder. If it is, you should be near a town. Yet there"s no hint of one. Night is closing in. And you"re low on gasoline. This is a situation where an in-car computer that can navigate would be a big help. A car computer that navigates? Yes! Such computers exist. Several experimental models are being tested by General Motors, Ford, Chrysler, and several foreign car makers. These computers vary in detail. But they all contain series of maps on videodiscs or videotapes. For example, one computer system contains 13,300 maps covering the continental US. Before starting out on a trip, a driver can type in the code for the region he or she plans to drive through. The computer then shows a map of that region. At the same time, a tiny radio receiver linked to the computer goes to work. It picks up signals from navigation satellites such as the NAVSTAR network. Using these signals, the computer shows the car"s position at all times and displays this position on the map. The computer can also calculate and display the best route to follow. A navigation computer may also receive and use data about road construction, weather conditions, and traffic jams. This information would be displayed to the driver and the computer would also use the information to work out alternate (交替的) routes. Most cars nowadays also contain computers that help cars run more efficiently. Microprocessors (微处理机) control certain engine functions by regulating the mixing of fuel. Data on car speed, oil pressure, revolutions per minute, engine temperature, and fuel level can be displayed as digital data (numbers) or warning lights. Some auto designers suggest that a central computer display be used to clearly present such timely information as car speed and fuel level. Warning lights would indicate a drop in oil pressure or a sudden rise in engine temperature. To get more information on these conditions, the driver could call it up on the computer display screen. When needed, the computer could be "asked" to provide navigation aid or information about the car"s condition.

单选题Which may NOT be a reason for higher cancer death rates among US blacks?

单选题It has been said that the Acts provided a new course of action and did not merely regulate or enlarge an old one.