问答题Flatfish, such as the flounder, are among the few vertebrates that lack approximate bilateral symmetry (symmetry in which structures to the left and right of the body's midline are mirror images). {{U}}Most striking among the many asymmetries evident in an adult flatfish is eye placement:{{/U}} before maturity one eye migrates, so that in an adult flatfish both eyes are on the same side of the head. While in most species with asymmetries virtually all adults share the same asymmetry, members of the starry flounder species can be either left-eyed (both eyes on the left side of head) or fight-eyed. {{U}}In the waters between the United States and Japan,{{/U}} the starry flounder populations vary from about 50 percent left-eyed off the United States West Coast, through about 70 percent left-eyed halfway between the United States and Japan, to nearly 100 percent left-eyed off the Japanese coast. {{U}}Biologists call this kind of gradual variation over a certain geographic range a "cline" and interpret clines as strong indications that the variation is adaptive, a response to environmental differences.{{/U}} For the starry flounder this interpretation implies that a geometric difference (between fish that are mirror images of one another) is adaptive, that left-eyedness in the Japanese starry flounder has been selected for, which provokes a perplexing questions: what is the selective advantage in having both eyes on one side rather than on the other? {{U}}The ease with which a fish can reverse the effect of the sidedness{{/U}} of its eye asymmetry simply by turning around {{U}}has caused biologists to study internal anatomy, especially the optic nerves, for the answer.{{/U}} In all flatfish the optic nerves cross, so that the right optic nerve is joined to the brain's left side and vice versa. This crossing introduces an asymmetry, as one optic nerve must cross above or below the other. G. H. Parker reasoned that if, for example, a flatfish's left eye migrated when the right optic nerve was on top, there would be a twisting of nerves, which might be mechanically disadvantageous. For starry flounders, then, the left-eyed variety would be selected against, since in a starry flounder the left optic nerve is uppermost. The problem with the above explanation is that the Japanese starry flounder population is almost exclusively left-eyed, an natural selection never promotes a purely less advantageous variation. As other explanations proved equally untenable, {{U}}biologists concluded that there is no important adaptive difference between left-eyedness and right-eyedness, and that the two characteristics are genetically associated with some other adaptively significant characteristic.{{/U}} This situation is one commonly encountered by evolutionary biologists, who must often decide whether a characteristic is adaptive or selectively neutral. As for the left-eyed and right-eyed flatfish, their difference, however striking, appears to be an evolutionary red herring.

问答题Although, recent years have seen substantial reductions in noxious pollutants from individual motor vehicles, the number of such vehicles has been steadily increasing consequently, {{U}}more than 1O0 cities in the United States still have levels of carbon monoxide, particulate matter, and ozone{{/U}} (generated by photochemical reactions with hydrocarbons from vehicle exhaust) {{U}}that exceed legally established limits.{{/U}} {{U}}There is a growing realization that the only effective way to achieve further reductions in vehicle emissions{{/U}}—short of a massive shift away from the private automobile—{{U}}is to replace conventional diesel fuel and gasoline with cleaner-burning fuels{{/U}} such as compressed natural gas, liquefied petroleum gas, ethanol, or methanol. {{U}}All of these altematives are carbon-based fuels whose molecules are smaller and simpler than those of gasoline.{{/U}} These molecules burn more cleanly than gasoline, in part because they have fewer, if any, carbon-carbon bonds, and the hydrocarbons they do emit are less likely to generate ozone. The combustion of larger molecules, which have multiple carbon-carbon bonds, involves a more complex series of reactions. These reactions increase the probability of incomplete combustion and are more likely to release uncombusted and photochemically active hydrocarbon compounds into the atmosphere. {{U}}On the other hand, alternative fuels do have drawbacks. Compressed natural gas would require that vehicles have a set of heavy fuel tanks{{/U}}—a serious liability in terms of performance and fuel efficiency—{{U}}and liquefied petroleum gas faces fundamental limits on supply.{{/U}} {{U}}Ethanol and methanol, on the other hand, have important advantages over other carbon-based alternative fuels:{{/U}} they have a higher energy content per volume and would require minimal changes in the existing network for distributing motor fuel. {{U}}Ethanol is commonly used as a gasoline supplement, but it is currently about twice as expensive as methanol,{{/U}} the low cost of which is one of its attractive features. Methanol's most attractive feature, however, is that it can reduce by about 90 percent the vehicle emissions that form ozone, the most serious urban air pollutant. Like any alternative fuel, methanol has its critics. Yet much of the criticism is based on the use of "gasoline clone" vehicles that do not incorporate even the simplest design improvements that are made possible with the use of methanol. It is true, for example, that a given volume of methanol provides only about one-half of the energy that gasoline and diesel fuel do; other things being equal, the fuel tank would have to be somewhat larger and heavier. However, since methanol-fueled vehicles could be designed to be much more efficient than "gasoline clone" vehicles fueled with methanol, they would need comparatively less fuel. {{U}}Vehicles incorporating only the simplest of the engine improvements that methanol makes feasible would still contribute to an immediate lessening of urban air pollution.{{/U}}

问答题与其关注学校应该要求学生做什么，不如质问学校能够为学生做什么。

As concerns over man's impact on the global environment increase, many interesting innovations are being considered. For example, "green roofs" - plant-filled roof top gardens - are one substantial way to confront the country's ecological problems, and there seems to be very little in the way of a downside. For one thing, a green roof acts as a sponge for rainwater, absorbing the majority of water from a typical rainstorm. Only three to five inches of soil for a green roof is sufficient for this to occur, which keeps the weight of the roof to a minimum. Because the plantings on the roof absorb the rainwater, drainage and sewage systems have a decreased volume of water pumping through them, keeping these systems from becoming over-stressed. And while, the soil and plants are absorbing rainwater, they are also taking in pollutants for their own nourishment by storing carbon and then emitting necessary oxygen back into the atmosphere.

For generations, Native Americans used myths and legends to explain the mysterious world around them. One such etiological myth originated with the Cherokee. According to the tale, at one time, far in the past, animals, birds, fishes, and even insects were able to communicate with one another. When humans arrived, however, life became more difficult because the creatures" habitats began to shrink. In order to protect themselves, the creatures decided to introduce disease to humans. The plant world, however, took sympathy upon the Cherokee and so provided a remedy for each of the diseases created by the creatures. It was because of this, says the legend, that the Cherokee turned to plants for antidotes and medicines for illness.

{{U}}Directions:{{/U}} In the following questions, choose the best answer from the five choices listed.

Reading Comprehension Questions {{U}}Directions:{{/U}} Multiple-choice Questions--Select One Answer Choice: These are the traditional multiple-choice questions with five answer choices from which you must select one. Multiple-choice Questions--Select One or More Answer Choices: These questions provide three answer choices; select all that are correct. Select-in-Passage: Choose the sentence in the passage that meets a certain description. Text Completion Questions {{U}}Directions:{{/U}} Select one entry from the corresponding column of choices for each blank. Fill all blanks in the way that best completes the text. Sentence Equivalence Questions {{U}}Directions:{{/U}} Select the two answer choices that, when used to complete the sentence, fit the meaning of the sentence as a whole and produce completed sentences that are alike in meaning. During the mid-twentieth century the United States began a policy toward Native Americans called "readjustment." This policy stemmed from the rise of the civil rights movement. Because of the movement, there was greater awareness that all Americans needed to be able to exercise the rights guaranteed by the United States Constitution. Readjustment recognized that life on reservations prevented Native Americans from exercising those rights. Reservations had created segregation that caused just as much damage as the racially segregated schools still prevalent throughout the nation during the period. The readjustment movement advocated the end of the federal government's involvement in Native American affairs and encouraged the assimilation of Native Americans into mainstream American society. The belief was that if it were beneficial for African American children to be placed in schools with white children, it would also be beneficial for Native Americans to become integrated into white society. The policy, however, failed to recognize the emergence of a new generation of Native American leadership and efforts to develop tribal institutions and reaffirm tribal identity. The new leadership did not desire assimilation, but instead wanted more segregation. The Native American community was vying to reassert its distinct identity and separate itself from mainstream America.

For Questions 16 through 20, select the two answer choices that, when used to complete the sentence, fit the meaning of the sentence as a whole and produce completed sentences that are alike in meaning.

See the diagram on the following page for information to answer the questions.

(A)5(B)10(C)15(D)25(E)Itcannotbedeterminedfromtheinformationgiven.

It ended with a whimper rather than a bang, plagued by debt, allegations of abuse, and the death of its founder. Yet in its day, the Boys Choir of Harlem was a marvel of precision and vocal superiority, and its boys traveled the world. Dr. Walter Turnbull organized the choir at his church in Harlem in 1968. Within a few years, the choir had its own school, where hundreds of children received training in academics and music. The choir performed at the White House and sang for the pope. It recorded music for award-winning films. Its demise troubles its alumni and former board members, but no one seems able to resurrect the lifeless organization. Underline the sentence that presents the author"s perspective on the original Boys Choir.

Far more (i) ______ than the counterfeiting of money or bonds is the counterfeiting of consumer goods, especially those that are popular and costly but easy to (ii) ______ cheaply; this is a worldwide and fairly open phenomenon. Blank (i) A. clandestine B. intricate C. prevalent Blank (ii) D. reproduce E. advertise F. sanction

For Questions 5 to 7, select one entry from the corresponding column of choices for each blank. Fill all blanks in the way that best completes the text.

Sending a robot into space to gather information is a viable option, but should only be regarded as that--an option. Even the most technologically advanced robots cannot and should not replace manned missions to outer space. Certainly it is cheaper and less dangerous to launch a computer probe that can gather reams of data, but often the information obtained by a machine only serves to produce more questions than it answers. Therefore, the space program should allow manned missions to follow up on those initial information-gathering robotic ventures. While manned missions are more costly than are unmanned missions, they are also more successful. Robots and astronauts use much of the same equipment in space, but a human is more capable of calibrating those instruments correctly and placing them in appropriate and useful positions. A computer is often neither as sensitive nor as accurate as a human in managing the same terrain or environmental circumstances. Robots are also not as equipped as humans to solve problems as they arise, and robots often collect data that is not helpful or even desired. A human, on the other hand, can make instant decisions about what to explore further and what to ignore.

DatafromthelnternetHockeydatabase;salariesfromHockeyZonePlus.

It"s such a ______ concept that it seems to have been around for all time, but packaged sliced bread has only been available since the late 1920s.