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维生素A只存在于动物性食物中，但也可由植物性食物转变而来。( )
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Like fine food, good writing is something we approach with pleasure and enjoy from the first taste to the last. And good writers, like good cooks, do not suddenly appear full-blown. Quite the contrary, just as the cook has to undergo an intensive training, mastering the skills of his trade, the writer must sit at his desk and devote long hours to achieving a style in his writing, whatever its purpose-schoolwork, matters of business, or purely social communication. You may be sure that the more painstaking the effort, the more effective the writing, and the more rewarding.There are still some remote places in the world where you might find a public scribe to do your business or social writing for you, for a fee. There are a few managers who are lucky enough to have the service of that rare kind of secretary who can take care of all sorts of letter writing with no more than a quick note to work from. But for most of us, if there is any writing to be done, we have to do it ourselves.We have to write school papers, business papers or home papers. We are constantly called on to put words to paper. It would be difficult to count the number of such words, messages, letters, and re- ports put into the mails or delivered by hand, but the daily figure must be enormous. What is more, everyone who writes expects, or at least hopes, that his writing will be read. We want to arouse (引起) and hold the interest of the readers. We want whatever we write to be read, from first word to last, not just thrown into some "letters-to-be-read" file (档案) or into a wastepaper basket. This is the reason we bend our efforts toward learning and practicing the skills of interesting, effective writing. According to the author, if your letter is thrown into some "letters-to-be-read" file,（）
在现金流量分析的指标中，最能反映企业举债能力的指标是经营现金流量净额与债务总额之比。（）
After the violent earthquake that shook Los Angeles in 1994, earthquake scientists had good news to report: The damage and death toll could have been much worse.More than 60 people died in this earthquake. (26) comparison, an earthquake of similar intensity that shook America in 1988 (27) 25,000 victims. (28) and deaths were relatively less in Los Angeles because the quake occurred at 4:31 a.m. on a holiday, (29) traffic was light on the city’s highways. In addition, changes made to the construction codes in Los Angeles during the last 20 years have (30) the city’s buildings and highways, making them more (31) to quakes.Despite the good news, civil engineers aren’t (32) on their successes. (33) to their drawing boards are blueprints for improved quake-resistant buildings. The new designs should (34) even greater security to cities where earthquakes often take place.In the past, making structures quake-resistant meant final yet (35) materials, such as steel and wood, which (36) without breaking. Later, people tried to lift a building off its foundation, and (37) rubber and steel between the building and (38) foundation to reduce the (39) of ground vibrations. The most recent designs give buildings (40) as well as concrete and steel supports. Called smart buildings, the structures (41) like living organisms to an earthquake’s vibrations. When the ground shakes and the building (42) forward, the computer would force the building to (43) in the opposite direction.The new smart structures could be very (44) to build. However, they would (45) many lives and would be less likely to be damaged during earthquakes. 36（）
Oceanography has always been regarded as the science of our oceans mixing geology, biology, chemistry, and physics to unveil the secrets of our seas. Scientists once defined oceanography as "the application of all sciences to the study of the sea". Before the nineteenth century, very few scientists showed an interest in the sea. Newton, a well-known scientist, explored some aspects of it theoretically in his works at one time, but later he was unwilling to have a further study on it.The sea was remote for the majority of the people, and except early travelers who traveled among continents or others who earned a living by undersea living creatures, it was not necessary to raise questions about it, let alone to ask what lay beneath the surface. Just when Europe and America proposed to lay a telegraph cable between them, the question "what is at the bottom of the seas" had to be answered for the first time with some commercial links. The engineers had to observe and measure the depth profile of the route to estimate the length of the cable to be produced.Thanks to Maury, the US Navy, the Atlantic Telegraph Company acquired information on this matter in 1853. In the 1840s, Maury had been assigned to encourage voyages during which soundings (测声) could be used to investigate the depths of the North Atlantic and Pacific Oceans as well. Later, some of his findings drew much attention and gained popularity in his book The Physical Geography of the Sea. The cable was laid, but the connection was not made permanent and reliable until 1866. At the early attempts, the cable failed and when it was taken out for repairs, it was found to be covered with living growths. The fact once refuted scientific argument at that time that there was no life in the deeper parts of the sea.Oceanography was gradually developed in next few years. In 1872 Thomson led a scientific expedition(考查) lasting for four years and brought back thousands of samples from the sea. Scientists were devoted to the classification and analysis of these samples for years and produced a five-volume report with the last volume published in 1895. The reason why Europe and America proposed to lay a telegraph cable was largely due to（）
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