单选题They need to move to new and large apartments. Do you know of any______ones in this area?

单选题In most earthquakes the Earth's crust cracks like porcelain. Stress builds up until a fracture forms at the depth of a few kilometers and the crust slips to relieve the stress. Some earthquakes, however, take place hundreds of kilometers down in the Earth's mantle, where high pressure makes rock so ductile that it flows instead of cracking, even under stress severe enough to deform it like putty. How can there be earthquakes at such depths? ' That such deep events do occur has been accepted only since 1927, when the seismologist Kiyoo Wadati convincingly demonstrated their existence. Instead of comparing the arrival times of seismic waves at different locations, as earlier researchers had done, Wadati relied on a time difference between the arrival of primary (P)waves and the slower secondary (S) waves. Because P and S waves travel at different but fairly constant speeds;the interval between their arrivals increases in proportion to the distance from the earthquake focus, or a rupture point For most earthquakes, Wadati discovered, the interval was quite short near the epicenter, the point on the surface where shaking is the strongest For a few events, however, the delay was long enough at the epicenter. Wadati saw a similar pattern when he analyzed data on the intensity of shaking. Most earthquakes had a small area of intense shaking, which weakened rapidly with increasing distance from the epicenter, but others were characterized by a lower peak intensity, felt over a broader area. Both the P-S intervals and the intensity patterns suggested two kinds of earthquakes: the more common shallow events, in which the focus lay just under the epicenter, and the deep events, with a focus several hundred kilometers down. The question remained;how can such quakes occur, given that mantle rock at a depth of more than 50 kilometers is too flexible to store enough stress to fracture? Wadati's work suggested that deep events occur in areas(now called Wadati-Benioff zones) where one crustal plate is forced under another and descends into the mantle. The descending rock is substantially cooler than the surrounding mantle and hence is less ductile and much more liable to fracture.

单选题The new government has just set up a {{U}}monopoly{{/U}} in salt.

单选题When a disease of epidemic proportions rips into the populace, scientists immediately get to work, trying to locate the source of the affliction and find ways to combat it. Oftentimes, success is achieved, as medical science is able to isolate the parasite, germ or cell that causes the problem and finds ways to effectively kill or contain it. In the most serious of cases, in which the entire population of a region or country may be at grave risk, it is deemed necessary to protect the entire population through vaccination, so as to safeguard lives and ensure that the disease will not spread. The process of vaccination allows the patient"s body to develop immunity to the virus or disease so that, if it is encountered, one can fight it off naturally. To accomplish this, a small weak or dead strain of the disease is actually injected into the patient in a controlled environment, so that his body"s immune system can learn to fight the invader properly. Information on how to penetrate the disease"s defenses is transmitted to all elements of the patient"s immune system in a process that occurs naturally, in which genetic information is passed from cell to cell. This makes sure that, should the patient later come into contact with the real problem, his body is well equipped and trained to deal with it, having already done so before. There are dangers inherent in the process, however. On occasion, even the weakened version of the disease contained in the vaccine proves too much for the body to handle, resulting in the immune system succumbing, and, therefore, the patient"s death. Such is the case of the smallpox vaccine, designed to eradicate the smallpox epidemic that nearly wiped out the entire Native American population and killed massive numbers of settlers. Approximately 1 in 10,000 people who receives the vaccine contract the smallpox disease from the vaccine itself and dies from it. Thus, if the entire population of the United States were to receive the Smallpox Vaccine today, 3000 Americans would be left dead. Fortunately, the smallpox virus was considered eradicated in the early 1970"s, ending the mandatory vaccination of all babies in America. In the event of a re-introduction of the disease, however, mandatory vaccinations may resume, resulting in more unexpected deaths from vaccination. The process, which is truly a blessing, may indeed hide some hidden cures.

单选题Several loudspeakers are______from the ceiling and we can hear the speaker very clearly.

单选题Alone in London, without friends, work or money, Shelley fell into______.

单选题The Japanese personnel manager had to______keeping a chemist on the payroll even though the company no longer needed his expertise.

单选题Most people don't think of a stamp as a receipt, but that is ______ it really is a proof of just how much money you have paid in advance for mail delivery. A. what B. why C. how D. who

单选题In the dark they could not see anything clear, but could ______.

单选题The primary objective of Basic Econometric, is to provide an elementary but a comprehensive introduction to the art and science of econometrics.

单选题Whether a person likes a routine office job or not depends largely on {{U}}temperament{{/U}}.

单选题Have you ever felt your life go into slow motion as you realize something bad is happening? You might have just knocked over a wine glass or noticed a car hurtling towards you, for example. Now scientists have measured exactly how much these attention-grabbing events slow down our perception of the world around us. Another example of the world appearing to slow down is when you are hanging on the phone waiting for someone to pick up at the other end. If your attention wanders while you're waiting then suddenly switches back, you will probably hear what seems like a longer than usual silence before hearing the dialing tone again. For you, time will have momentarily slowed. To see how our perception of time changes when something new happens, Vincent Walsh and his colleagues put headphones on volunteers and played eight beeps to their right ears. The gap between each beep was exactly 1 second, except for the gap between the fourth and fifth beeps, which the scientists could make shorter or longer. They altered the length of this gap until the volunteers estimated it was the same length as the other gaps. The researchers found that, on average, people judge a second slightly short, at 955 milliseconds. In the second part of the experiment, the first four beeps were played to the subjects' right ears, but the other four were then played to their left. Again, the volunteers were asked to estimate when the gap between the fourth and fifth beeps was the same as the others. This time they judged a second to be even shorter at 825 milliseconds long. Perceiving a second to be much shorter than it is makes you feel as though the world has gone into slow motion, since less happens in that slice of time. Walsh thinks the effect could have evolved to give us a fraction more time to react to potentially threatening events. Last year, Kielan Yarrow, a British psychologist found a similar effect with vision. When you glance at a clock, the first second will seem longer than it really is. Yarrow's results showed that time appeared to slow down by a similar amount as Walsh found. Previous studies have shown that cooling the body slows down our perception of time while warming it up has the opposite effect.

单选题A boy 6 feet tall and weighing only 130 pounds is very ______.

单选题 The explosion of a star is an awesome event. The most violent of these cataclysms, which produce supernovae, probably destroys a star completely. Within our galaxy of roughly 100 billion stars the last supernova was observed in 1604. Much smaller explosions, however, occur quite frequently, giving rise to what astronomers call novae and dwarf novae. On the order of 25 novae occur in our galaxy every year, but only two or three are near enough to be observed. About 100 dwarf novae are known altogether. If the exploding star is in a nearby part of the galaxy, it may create a "new star" that was not previously visible to the naked eye. The last new star of this sort that could be observed clearly from the Northern Hemisphere appeared in 1946. In these smaller explosions the star loses only a minute fraction of its mass and survives to explode again. Astrophysicists are fairly well satisfied that they can account for the explosions of supernovae. The novae and dwarf novae have presented more of a puzzle. I shall describe recent investigations that have provided important new information about these two classes of exploding star. The picture that emerges is quite astonishing. It appears that every dwarf nova--and perhaps every nova--is a member of a pair of stars. The two stars are so close together that they revolve around a point that lies barely outside the surface of the larger star. As a result the period of rotation is usually only a few hours and their velocities range upward to within a two-hundredth the speed of light, Astronomers use the term "cataclysmic variable" to embrace the three general classes of exploding star: dwarf novae, novae, and supernovae. A cataclysmic variable is defined as a star that suddenly and unpredictably increases in brightness by a factor of at least 10. Dwarf novae are stars that increase in brightness by factor of 10 to 100 within a period of several hours and decline to their former brightness in two or three days. In this period they emit some 1038 to 1039 ergs of energy. At maximum brilliance a dwarf nova shines about as intensely as our sun, previously it had been only about a hundredth as bright. The number of outbursts ranges anywhere from 3 to 30 a year, but for any one star the intervals have a fairly constant value. Moreover, the maximum bright ness from outburst to outburst is the same within a factor of two for a given star. The dwarf novae are often referred to, after their prototypes, as U Geminornm or SS Cygni stars. (The stars of each constellation are designated by letters or numbers.) A subgroup of dwarf novae, called Z Camelopardalis stars, do not always descend to minimum bright ness between outbursts but may stay at some intermediate level for several months.

单选题The author made a few minor adjustments and then______.

单选题When Graham didn't come home from school, we were very worded about him. But fortunately he came to no ______.

单选题The conditions can be well imagined when one small settlement is expected to ______ 10,000 families. A. populate B. dwell C. house D. reside

单选题The sense of trust in an infant is under development when ______.

单选题To their great surprise, they found the floodwater had Udamaged/U the building's foundation.