[外语类试卷]大学英语六级改革适用(阅读)模拟试卷258及答案与解析.doc
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1、大学英语六级改革适用(阅读)模拟试卷 258及答案与解析 Section C 0 Most growing plants contain much more water than all other materials combined. C. R. Barnes has suggested that it is as proper to term the plant a water structure as to call a house composed mainly of brick a brick building. Certain it is that all essential p
2、rocesses of plant growth and development occur in water. The mineral elements from the soil that are usable by the plant must be dissolved in the soil solution before they can be taken into the root. They are carried to all parts of the growing plant and are built into essential plant materials whil
3、e in a dissolved state. The carbon dioxide (CO2) from the air may enter the leaf as a gas but is dissolved in water in the leaf before it is combined with a part of the water to form simple sugars the base material from which the plant body is mainly built Actively growing plant parts are generally
4、75 to 90 percent water. Structural parts of plants, such as woody stems no longer actively growing, may have much less water than growing tissues. The actual amount of water in the plant at any one time, however, is only a very small part of what passes through it during its development. The process
5、es of photosynthesis, by which carbon dioxide and water are combined in the presence of chlorophyll (叶绿素 ) and with energy derived from light to form sugars, require that carbon dioxide from the air enter the plant. This occurs mainly in the leaves. The leaf surface is not solid but contains great n
6、umbers of minute openings, through which the carbon dioxide enters. The same structure that permits the one gas to enter the leaf, however, permits another gas water vapor to be lost from it. Since carbon dioxide is present in the air only in trace quantities (3 to 4 parts in 10,000 parts of air) an
7、d water vapor is near saturation in the air spaces within the leaf (at 80F, saturated air would contain about 186 parts of water vapor in 10,000 parts of air), the total amount of water vapor lost is many times the carbon dioxide intake. Actually, because of wind and other factors, the loss of water
8、 in proportion to carbon dioxide intake may be even greater than the relative concentrations of the two gases. Also, not all of the carbon dioxide that enters the leaf is synthesized into carbohydrates (碳水化合物 ). 1 A growing plant needs water for all of the following except_. ( A) forming sugars ( B)
9、 sustaining woody stems ( C) keeping green ( D) producing carbon dioxide 2 The essential function of photosynthesis in terms of plant needs is _. ( A) to form sugars ( B) to derive energy from light ( C) to preserve water ( D) to combine carbon dioxide with water 3 The second paragraph uses facts to
10、 develop the essential idea that _. ( A) a plant efficiently utilizes most of the water it absorbs ( B) carbon dioxide is the essential substance needed for plant development ( C) a plant needs more water than is found in its composition ( D) the stronger the wind, the more the water vapor loss 4 Fr
11、om the passage, we learn that_. ( A) the mineral elements will not be absorbed by the plant unless they are dissolved in its root ( B) the woody stems contain more water than the leaves ( C) air existing around the leaf is found to be saturated ( D) only part of the carbon dioxide in the plants is s
12、ynthesized 5 This passage is mainly about_. ( A) the functions of carbon dioxide and water ( B) the role of water in a growing plant ( C) the process of simple sugar formation ( D) the synthesis of water with carbon dioxide 5 Birds that are literally half-asleep with one brain hemisphere alert and t
13、he other sleeping control which side of the brain remains awake, according to a new study of sleeping ducks. Earlier studies have documented half-brain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled
14、by the sleeping hemisphere keeps shut, while the wakeful hemispheres eye stays open and alert. Birds also can sleep with both hemispheres resting at once. Decades of studies of bird flocks led researchers to predict extra alertness in the more vulnerable, end-of-the-row sleepers. Sure enough, the en
15、d birds tended to watch carefully on the side away from their companions. Ducks in the inner spots showed no preference for gaze direction. Also, birds dozing (打盹 ) at the end of the line resorted to single-hemisphere sleep, rather than total relaxation, more often than inner ducks did. Rotating 16
16、birds through the positions in a four-duck row, the researchers found outer birds half-asleep during some 32 percent of dozing time versus about 12 percent for birds in internal spots. “We believe this is the first evidence for an animal behaviorally controlling sleep and wakefulness simultaneously
17、in different regions of the brain,“ the researchers say. The results provide the best evidence for a long-standing supposition that single-hemisphere sleep evolved as creatures scanned for enemies. The preference for opening an eye on the lookout side could be widespread, he predicts. Hes seen it in
18、 a pair of birds dozing side-by-side in the zoo and in a single pet bird sleeping by a mirror. The mirror-side eye closed as if the reflection were a companion and the other eye stayed open. Useful as half-sleeping might be, its only been found in birds and such water mammals (哺乳动物 ) as dolphins, wh
19、ales, and seals. Perhaps keeping one side of the brain awake allows a sleeping animal to surface occasionally to avoid drowning. Studies of birds may offer unique insights into sleep. Jerome M. Siegel of the UCLA says he wonders if birds half-brain sleep “is just the tip of the iceberg (冰山 ).“ He sp
20、eculates that more examples may turn up when we take a closer look at other species. 6 A new study on birds sleep has revealed that _. ( A) half-brain sleep is found in a wide variety of birds ( B) half-brain sleep is characterized by slow brain waves ( C) birds can control their half-brain sleep co
21、nsciously ( D) birds seldom sleep with the whole of their brain at rest 7 According to the passage, birds often half sleep because _. ( A) they have to watch out for possible attacks ( B) their brain hemispheres take turns to rest ( C) the two halves of their brain are differently structured ( D) th
22、ey have to constantly keep an eye on their companions 8 The example of a bird sleeping in front of a mirror indicates that _. ( A) the phenomenon of birds dozing in pairs is widespread ( B) birds prefer to sleep in pairs for the sake of security ( C) even an imagined companion gives the bird a sense
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