单选题According to the passage, it is believed that the largest extinction of a species occurred

单选题The word "rotting" in line 4 is closest in meaning to

单选题The word "exercise" in line 15 is closest in meaning to

单选题......... crumbles readily when exposed to a moist, acid atmosphere, but the stone is durable in a dry atmosphere.

单选题Henry Ford Henry Ford was born in 1863 on a farm near Dearborn, Michigan and is best known for his pioneering efforts in the automobile industry. Ford"s beginnings in that industry were humble as he became a machinist"s apprentice in Detroit at age 16 and then worked for much of the 1890s as a mechanical engineer. During his leisure hours, he experimented with the construction of the first automobile, which he achieved in 1896 with the Quadricycle. In 1903, he founded the Ford Motor Company. Ford is perhaps most famous for producing the Model T in 1913. This car was revolutionary in its use of interchangeable parts and assembly line techniques during its production. While Ford was not the first to use these practices, he was the first to implement them on a large scale, and this led to the great expansion of the Ford Motor Company and American industry in general. Ford"s innovative production techniques had their downside, however, as by early 1914 the monthly labor turnover at the Ford plant was almost 50% due to low wages, heavy workloads and the monotony of the assembly line. He responded by doubling the daily wage that was then standard in the industry to almost $5 per day. This stabilized the workforce and resulted in a reduction in operating costs. The increase in workers" wages also raised their standard of living and made it possible for them to be consumers of cars and other durable goods, which further spurred production. The Model T was discontinued in 1927 after having sold 15 million cars. While Ford was the pioneer in the mass production of cars, he was slow to respond to the trend in the industry for new models to be introduced each year. Consequently, Ford"s position as the preeminent producer and seller of automobiles was lost to the competition such as General Motors. Ford did not adopt the practice of yearly changes in models until the 1930s, and by then the company had lost the early lead it had enjoyed over its competitors. While Ford is best known for introducing the Model T and mass automobile production, his company also manufactured airplanes, particularly during World War Ⅱ. Ford also made a name for himself as a politician as he ran for a seat in the U.S. Senate in 1918, but was defeated. As a private citizen, he took on the role of statesman and traveled to Europe in 1915 with a number of like-minded others with the purpose of trying to persuade the warring European countries to put an end to the First World War. Ford was also a noted philanthropist as he built one of the most expensive hospitals in the world in Detroit in 1919. Upon his death in I947, he left the bulk of his personal fortune of over $600 million to the non-profit Ford Foundation. Glossary assembly line: mechanical system in a factory whereby an article is conveyed through sites at which successive operations are performed on it apprentice: one who is learning a trade or occupation statesman: a man who is a respected leader in national or international affairs foundation: an institution supported by an endowment

单选题In paragraph 3, the author makes which of the following statements about a species' survival?

单选题Diamond is the hardest known substance, so diamond can be cut only by another diamonds.

单选题Solving Sudoku Puzzles The principle behind Sudoku puzzles is fairly straightforward. A typical Sudoku grid is made up of nine rows and nine columns containing 81 individual cells. This basic fiat square grid is further divided into nine smaller 3X3 squares called sub-grids. Each sub-grid thus consists of its own nine cells. At the beginning of the puzzle some numbers are already printed in certain cells. A player must completely fill in the empty cells with numbers ranging from the 1 to 9 so that no digit appears in the same row, column or subgrid twice. Any Sudoku puzzle has only one possible solution. In spite of the fact that it is an analytical game involving numbers, it does not require any mathematical skills because no arithmetic operations assist players in completing the grid. This must be why Sudoku puzzles are all the rage amongst logic games right now. Not since the three-dimensional Rubik cube of the 1980s has a game attracted more players. But, unlike its modern times predecessor, Sudoku dates way back to the Middle Ages, when so-called Latin squares were being filled up with icons or colors instead of numbers. The German mathematician Leonard Euler was the first scientist to draw attention to these number-games and study their rules during the 18th century. The first printed Sudoku puzzle appeared in the May 1979 edition of "the Dell Pencil Puzzles and Word Gaines" under the care of retired architect Howard Garns. But the name Sudoku derives from its 1984 Japanese translation in a magazine, and means something like "single numbers." A Hong Kong retired judge named Wayne Gould came across one such puzzle during a visit to Japan in 1997 and proceeded to write a computer program that would automatically generate Sudoku grids. He managed to publish a stream of such puzzles in two major London newspapers during 2004-2005, and thus a new craze was to be born. At the moment, no respectable magazine or even weekend flyer can hope to sell if it does not include a Sudoku. The game is more often than not played online too, and there are dedicated websites that cater to any Sudoku aficionado. From novice to diabolical grids, computer programs can pretty much spew out any puzzle as one"s heart desires. For those fans already bored by the traditional grid, there are several compelling alternatives. The Dum-Sum-Oh puzzle replaces numbers with letters or dominoes, and square sub-grids with other types of geometric shapes. In another variant, six triangular sub-grids intertwine to add numerical challenge, or else three game boards overlap for even more complexity. Further complications can be added by requiring players to perform side-by-side mathematical operations, or by making use of the "greater-than-less-than" signs. Thus, a Sudoku can take anywhere from a few minutes to several hours to complete. But it is not only players who got obsessed with Sudoku. Mathematicians have also started to analyze a host of fascinating issues that Sudoku raises. They have yet to solve the question of how many Sudoku starting grids exist. They are also still scratching their heads about the smallest number of start-up digits in a grid that can still guarantee a single solution, although the answer seems to be 17 after 16 was ruled out. It is very time-consuming to verify this answer since there are over 5 trillion valid Sudoku puzzles out there although their total number had not been identified yet. Even a speedy and proficient computer program would need something close to 173 years to check for all possibilities. One thing is for certain, nonetheless. The maximum number of givens to guarantee a unique solution is 77. Glossary grid: network of evenly spaced horizontal and vertical lines that can be superimposed on a map, chart, etc., especially in order to locate specific points variant: an example that differs from a standard a host of: a very large number of

单选题The passage supports which of the following statements about the Surveyor and Apollo missions?

单选题Which of the following phrases is defined in paragraph 1 ?

单选题According to the passage, the imbalances discussed in paragraph 3 may have resulted from

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单选题Listening6"GeologyClass"

单选题In so-called nonfiction novels, a documentary style is combined with fictional techniques ______ actual events and people.

单选题It is a popular notion that autumn leaves are tinted by freezing temperatures. In truth, the foliage is dulled, not colored, by frost. Red leaves such as maples are brightest when sunny days are followed by cool--but not freezing--nights. Under such conditions, sun- made sugars are trapped in the leaves, where they form the red pigment anthocyanin. Leaves that appear yellow in autumn are no less yellow in spring and summer. However, in spring and summer the yellow pigments--carotenoid and xanthophyll--are masked by the green pigment chlorophyll, which breaks down with the diminishing sunlight of fall.

单选题The word "sums" in line 20 is closest in meaning to

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单选题It was (not until) after Emily Dickinson's death in 1886 that, (hidden away) in her bureau, (overly) one thousand unpublished poems (were discovered)

单选题Mostocean waves are generatedby wind current that agitate the water's surface.

单选题Pheromone systems are relatively complex in insects that