In significant parts of Eurasia, the middle centuries of the first millennium__a significant transition in human cultural history.

A.define

B.mark

C.identify

D.specify

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The degree of a beach's downward slope depends on its composition of deposits as well as on the action of waves across its surface.

A.sediments

B.segments

C.substances

D.sources

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The one word that sums up the attitude of the silent filmmaker is enthusiasm, conveys most strongly before formulas took shape and when there was more room for experiments.

A.conveyed

B.conveying

C.to convey

D.being conveyed

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There is something intrinsically fascinating about the idea of evolution. What principles govern the evolution of a species? And what does evolution tell us about the place of Homosapiens in the grand order of things? The writer George Bernard Shaw held that a mystical guiding force impels life to evolve toward eventual perfection. Modem scientists may not believe in this guiding force or in the possibility of perfection, but many would agree that life has been improving itself through evolution for billions of years. （Note that this conveniently makes Homosapiens, a very recent product of evolution, one of the newest and most improved versions of life.） In the view of these scientists, constant competition among species is the engine that drives the process of evolution and people's life upward.
To Darwin, nature was a surface covered with thousands of sharp wedges, all packed together and jostling for the same space. Those wedges that fared best moved toward the center of the surface, improving their position by knocking other wedges away with violent blows. The standard example that textbooks give of such competitive wedging is the interaction between the brachiopods and the clams. Clams were long held to be ancient undersea competitors of brachiopods due to the fact that the two species inhabited the same ecological niche. Clams are abundant today, whereas brachiopods （dominant in ancient times） are not. Modem clams are also physiologically more complex than brachiopods are.The standard interpretation of these facts is that the clams' physiology was an evolutionary improvement that gave them the ability to “knock away” the brachiopods.
In recent years, however, the prominent naturalists Stephen Jay Gould and C. Brad Calloway have challenged the validity of this example as well as the model it was meant to support. Gould and Calloway found that over most geological time clams and brachiopods went their separate ways. Never did the population of brachiopods dip as that of the clams rose, or vice versa. In fact, the two populations often grew simultaneously, which belies the notion that they were fighting fiercely over the same narrow turf and resources. That there are so many more clams than brachiopods today seems rather to be a consequence of mass deaths that occurred in the Permian period. Whatever caused the mass deaths---some scientists theorize that either there were massive ecological or geological changes, or a comet crashed down from the heavens — clams were simply able to weather the storm much better than brachiopods.
Out of these observations, Gould and Calloway drew a number of far-reaching conclusions. For instance, they suggested that direct competition between species was far less frequent than Darwin thought. Perhaps nature was really a very large surface on which there were very few wedges, and the wedges consequently did not bang incessantly against each other. Perhaps the problem facing these wedges was rather that the surface continually altered its shape, and they had to struggle independently to stay in a good position on the surface as it changed.
So where does that leave Homosapiens if evolution is a response to sudden, unpredictable and sweeping changes in the environment rather than the result of a perpetual struggle? No longer are we the kings of the mountain who clawed our way to the top by advancing beyond other species. We are instead those who looked to the mountains when floods began to rage below and then discovered that living high up has its definite advantages, so long as our mountain doesn't decide to turn into a volcano.

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The world’s greatest snow-capped peaks,which run in a chain from the Himalayas to the Tianshan Mountains on the border of China and Kyrgyzstan, have lost no ice over the last decade, new research shows.
The discovery has___（91） scientists, who had believed that around 50 billion tons of melted water were being shed each year and not being replaced by new snowfall.
The study is the first to survey all the world's icecaps and glaciers and was made___（92） by the use of satellite data. Overall, the___（93） of melting ice outside the two largest caps — Greenland and Antarctica — is much___（94） than previously estimated, with the lack of______（95） loss in the Himalayas and the other high___（96） of Asia responsible for most of the discrepancy.
Bristol University glaciologist Professor Jonathan Bamber said, “The very unexpected result was the______（97） mass loss from high mountains of Asia, which is not___（98） different from zero.”
The melting of Himalayan glaciers caused___（99） in 2009 when a report from the UN's Intergovernmental Panel on Climate Change mistakenly stated that they would disappear by 2035, instead of 2350.___（100）, the scientist who led the new work is clear that while greater uncertainty has been discovered in Asia’s highest mountains,the melting of icecaps and glaciers around the world______（101） a serious concern.
“Our results and those of everyone else show we are___（102） a huge amount of water into the oceans every year,” said Professor John Wahr of the University of Colorado.His team’s study concludes___（103） 443 to 629 billion tons of melted water overall are added to the worlds oceans each year. This is___（104） sea level by about 1.5 mm a year, the___（105） reports, in addition to the 2 mm a year caused by___（106） of the warming ocean.
The scientists are___（107） to point out that lower-altitude glaciers in the Asian mountain ranges are___（108） melting. Satellite images and reports___（109）this. But over the study period from 2003 to 2010, enough ice was added to the peaks to___（110）.

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