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Under certain circumstances, the human body must cope with gases at greater-than- nonnal atmospheric pressure. For example, gas pressures increase rapidly during a dive made with scuba gear because the breathing equipment allows divers to stay underwater longer and dive deeper. The pressure exerted on the human body increases by 1 atmosphere for every 10 meters of depth in seawater, so that at 30 meters in seawater a diver is exposed to a pressure of about 4 atmospheres. The pressure of the gases being breathed must equal the external pressure applied to the body; otherwise breathing is very difficult. Therefore all of the gases in the air breathed by a scuba diver at 40 meters are present at five times their usual pressure. Nitrogen, which composes 80 percent of the air we breathe, usually causes a balmy feeling of well-being at this pressure. At a depth of 5 atmospheres, nitrogen causes symptoms resembling alcohol intoxication, known as nitrogen narcosis. Nitrogen narcosis apparently results from a direct effect on the brain of the large amounts of nitrogen dissolved in the blood. Deep dives are less dangerous if helium is substituted for nitrogen, because under these pressures helium does not exert a similar narcotic effect.As a scuba diver descends, the pressure of nitrogen in the lungs increases. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues. The reverse occurs when the diver surfaces; the nitrogen pressure in the lungs falls and the nitrogen diffuses from the tissues into the blood, and from the blood into the lungs. If the return to the surface is too rapid, nitrogen in the tissues and blood cannot diffuse out rapidly enough and nitrogen bubbles are formed. They can cause severe pains, particularly around the joints.Another complication may result if the breath is held during ascent. During ascent from a depth of 10 meters, the volume of air in the lungs will double because the air pressure at the surface is only half of what it was at 10 meters. This change in volume may cause the lungs to distend and even rupture. This condition is called air embolism. To avoid this event, a diver must ascend slowly, never at a rate exceeding the rise of the exhaled air bubbles, and must exhale during ascent.1.The words “exposed to” in line 5 are closest in meaning to （）.2.It can be inferred from the passage that which of the following presents the greatest danger to a diver?3.What should a diver do when ascending?

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 a 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 star the intervals have a fairly constant value. Moreover, the maximum brightness 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 Geminorum 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 brightness between outbursts but may stay at some intermediate level for several months.1.The title below that best expresses the ideas of this passage is （）.2.The reason why dwarf novae explode is （）. 3.It is likely that in the paragraph that follows this passage the author will discuss （）. 4.It can be seen from the last paragraph of the passage that Z Camelopardalis stars are （）. 5.Astronomers are acquainted with approximately （）.

Each advance in microscopic technique has provided scientists with new perspective on the function of living organisms and the nature of matter itself. The invention of the visible-light microscope late in the sixteenth century introduced a previously unknown realm of single-celled plants and animals. In the twentieth century, electron microscopes have provided direct views of viruses and minuscule surface structures. Now another type of microscope, one that utilizes X-rays rather than light or electrons, offers a different way of examining tiny details; it should extend human perception still farther into the natural world.The dream of building an X-ray microscope dates to 1895; its development, however, was virtually halted in the 1940’s because the development of the electron microscope was progressing rapidly. During the 1940’s,electron microscopes routinely achieved resolution better than that possible with a visible-light microscope, while the performance of X-ray microscopes resisted improvement. In recent years, however, interest in X-ray microscopes has revived, largely because of advances such as the development of new sources of X-ray illumination. As a result, the brightness available today is millions of times that of X-ray tubes, which, for most of the century, were the only available sources of soft X-rays.The new X-ray microscopes considerably improve on the resolution provided by optical microscopes. They can also be used to map the distribution of certain chemical elements. Some can form pictures in extremely short times; others hold the promise of special capabilities such as three-dimensional imaging. Unlike conventional electron microscopy, X-ray microscopy enables specimens to be kept in air and in water, which means that biological samples can be studied under conditions similar to their natural state. The illumination used, so-called soft X rays in the wavelength range of twenty to forty angstroms (an angstrom is one ten-billionth of a meter), is also sufficiently penetrating to image intact biological cells in many cases. Because of the wavelength of the X rays used, soft X-ray microscopes will never match the highest resolution possible with electron microscopes. Rather, their special properties will make possible investigations that will complement those performed with light-and electron-based instruments.1.What is the theme does the passage mainly discuss?2.Why does the author mention the visible-light microscope in the first paragraph?3.Why did it take so long to develop the X-ray microscope?4.Based on the information in the passage, what can be inferred about X-ray microscopes in the future?

A near revolution has occurred over the past decade in our understanding of the impacts of climate change. Both the natural science and the economics underlying predictions of climate-change impacts have altered dramatically. Climate scientists have reduced the magnitude of predicted warming, suggesting milder future climate scenarios. Ecologists have shifted from predicting ecosystem collapse to predicting that net primary productivity will likely increase over the long run. And economists are no longer predicting large damages, but rather a mixture of damages and benefits.These changes are so dramatic that it is not clear whether the net economic effects from climate change over the next century will be harmflil or helpful. The new research further suggests that effects are likely to vary across the planet. We now expect temperate and polar countries to enjoy small economic gains, whereas tropical countries are more likely to suffer economic losses.Of course, we have not banished all uncertainty, which will always haunt future projections of outcomes. The dynamics of ecosystems are poorly understood; carbon cycles may change over time; polar ice may generate unwelcome surprises; and the effects of change on tropical regions have not yet had the thorough study they require. Nonetheless, the recent scientific and economic findings create a new perspective on the greenhouse-gas problem, and this new vision, in turn, calls for new strategies and new political outcomes.The reduction in damage-estimates removes the urgency to engage in costly crash abatement programs. Our initial perspective on greenhouse gases suggested that we were rapidly approaching the edge of a cliff. Those fears now appear unfounded, for the impacts from climate warming seem to be relatively small for the next century. There will be damages to be sure, but they will be offset by benefits. The net expected effect now is closer to zero rather than to 2 percent of GDP. As a consequence, the new abatement policies should be designed for the long run, and should be inexpensive and cost-effective.1.The overall purpose of the passage is to （）.2.The author suggests that the “new perspective” (Para. 3) is the result of a shift from （）. 3.The author of the passage would most likely agree that （）. 4.The author assumes that the reader（）.

James Joyce was an Irish novelist who revolutionized the methods of depicting characters and developing a plot in modern fiction. His astonishing way of (1) a novel, his frank portrayal of human (2) in his books, and his complete command of English have (3) him one of the outstanding influences on literature in the 20th century. Many (4) judge that he is second only to Shakespeare in his (5) of the English language. Joyce was deeply influenced by Ireland and (6) all his books about Dublin.When he was in Dublin College, he (7) languages and spent his spare time reading books. He (8) to take part in the nationalist (9) like his fellow students, but he became (10) interested in literature. He wrote outspoken (11) of literary criticism that shocked his teachers and even taught himself Norwegian so that he could read Ibsen’s works in the (12).When he graduated in 1902, he (13) he would become a writer and an (14), because he felt he could not be one (15) the other. In order to preserve his ideal of writing (16), fully, and as objectively as he knew how, (17) the people and places he knew best, he had to escape from all (18) to become involved in popular (19) or public life. He went to France, Italy and Switzerland, where he lived in (20) and obscurity for the first 20 years, only returning to Ireland when his mother was dying. Except for a couple of brief trips, he stayed abroad all his life.

But McConnell Moore has always drawn great strength from such cartoonish（）, which he collects and then displays on his Senate office wall.

At the same time, the public will not admit the random,（）alteration of plans, nor without complain the changeableness of plans.

Bill Clinton projected an（）personality in the 1992 campaign, but that was not his only advantage over Bush and an independent candidate, Ross Perot.

The woman wearing it could experience a change of personality similar to a fuzzy green caterpillar’s（）into a mature butterfly.

Besides cold temperatures, short growing seasons and heavy snows also prevent（）at high elevations.

One strategy is simply to persuade people to stay longer, which provides more time for employers to spot and（）the best performers.

A major goal of law of any country, to deter potential criminals by punishing wrongdoers, is not served when the penalty is so seldom invoked that it ceases to be a（）threat.

It is usually a good thing when a discussion is taken firmly by the hand and led down from the heights of to（）the level ground of hard fact.

The research suggests a wave of possible protectionism in 2010 as such investigations lead to the（）of anti-dumping penalties.

Today, we who read Latin return far more often to the exuberance of Apuleius than to the carefully molded（）of Cicero.

Whenever I worried that our connection might be fading, I opened the drawer and felt his energy（）around me like a freed canary.

The purchase of a new mansion and a brand-new automobile has become the（）of the new generation of white-collar worker along with their desire of holidays overseas.

If your goals are general, you should（）them（）into sub-goals, so that you have a schedule for each sub-goal too.

As serious as she is about the bullfight, she does not allow respect to（）her sense of whimsy when painting it.

Before about 1960, virtually all accounts of evolution assumed most adaptation to be a product of selection at the level of populations; recent studies of evolution, however, have found no（）this pervasive view of selection.

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