[外语类试卷]大学英语四级模拟试卷776及答案与解析.doc
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1、大学英语四级模拟试卷 776及答案与解析 一、 Part I Writing (30 minutes) 1 For this part, you are allowed 30 minutes to write a composition on the topic: Keeping Our City Clean. You should write at least 120 words and you should base your composition on the outline (given in Chinese) below: 1城市无论大小都应该保持清洁 2保持城市清洁不是一件容易的
2、事 3为了保持城市的清洁,我们的政府做了大量的工作 二、 Part II Reading Comprehension (Skimming and Scanning) (15 minutes) Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions attached to the passage. For questions 1-7, mark: Y (for YES) if the statement agrees with the in
3、formation given in the passage; N (for NO) if the statement contradicts the information given in the passage; NG (for NOT GIVEN) if the information is not given in the passage. 1 Flood Control As long as people live on the Earth they suffer from floods. Stories of great floods in ancient times-for e
4、xample, the Bible story of Noah and the Ark-have come down from many early peoples. Although floods are not increasing in size or frequency in the United States, damage from them, however, is increasing to such an extent that they are a major menace (威胁 ) to the national welfare (社会安全 ). Most large
5、cities and industries are situated on the seacoasts, on the shores of large lakes or on rivers. In the fiver valleys lie the richest farmlands and the easiest routes for railways and highways. Land subjected to flooding in the United States has been estimated at 50 million acres. As fast as they are
6、 supposedly protected by flood-control works, people move into flood plains. The population density on flood plains is more than twice the national average. Yet these areas cannot be given complete protection. The average annual property loss is in excess of one billion dollars. A single great flood
7、 in 1955 in six northeastern states caused property damage amounting to a half billion dollars. A flood induced by Hurricane Agnes in June 1972 caused property damage in the eastern United States that totaled about 3 billion dollars. One way to avoid floods is to take the obvious precaution of livin
8、g where there is no danger of high waters. The Bible story of The Tower of Babel tells of an attempt to escape flood damage in this way. To follow such a program, however, would compel people to leave many of their richest regions. It has always been convenient and often necessary to build homes and
9、 factories on the floodplains along rivers and streams and 6n the seacoasts. American pioneer settlers depended upon the streams for drinking water, transportation, and power to run their mills and factories. Floodplains, deep with the silt laid down by overflowing rivers, are fertile farmlands. The
10、 earliest towns and farms, therefore, were established along the riverfronts, and large portions of them were built on land that was subject to periodic flooding. While the communities were small, the damages suffered from floods were limited. With the great population and industrial growth of the U
11、nited States, flood damage has become a serious national problem. Two Approaches to Flood Control There are two basic approaches to flood control. One is to minimize the extent of flooding by building dams, reservoirs, levees (防洪堤 ), and other engineering works. The other is to prevent floods by con
12、servation practices designed to hold the water where it falls in the headstreams and watersheds. Engineers in ancient times built earthen mounds to keep back floodwater. Such artificial embankments (堤防 ), called levees, held Chinese rivers in check for centuries. This method was followed in colonial
13、 America. New Orleans built a levee for protection from the Mississippi River early in the 1700s. The states intensified levee construction on the Mississippi in about 1850. Modern Levee Building Because a levee at one point confines the water there and raises the peak of flood waters upstream and d
14、ownstream, levees once started usually have to be built at all the low points of a river system. Furthermore, a system of levees is only as strong as its weakest spot. Thus uniform height and strength are required. Only a government, which controls the river from end to end, can safely supervise lev
15、ee building. The Mississippi River has probably the longest continuous levees in the world. One extends from Pine Bluff, Ark., southward for 380 miles. To keep the current from eating away the levee surfaces, long-rooted Bermuda grass is thickly sown on them. They may also be covered with mats of wi
16、llow branches, with asphalt (沥青 ), or with a flexible mat of concrete blocks connected by reinforcing fabric and twist wire. Such coverings are called revetments (铺面 ,堑壕 ). They are also used to stabilize a rivers banks and keep the stream within its old channel. Floodways and Spillways Floodways (分
17、洪河道 ) divert excess water from the main river channel and carry it off by a different route. From Cairo, Ill., to New Madrid, Mo., for example, the high east-bank bluffs and the levees along the west bank create a narrow channel for the river. A setback levee was built about five miles west of the r
18、iver front levee. The strip between the setback and the riverfront levee is known as the Birds Point-New Madrid Floodway. At extremely high flood stages water enters the floodway through fuse plugs in the old riverfront levee near Cairo and reenters the main river just above New Madrid. The floodway
19、 was operated during the 1937 flood and was valuable in protecting Cairo from high water. There are three other floodways on the lower Mississippi. About 35 miles above New Orleans flood waters can be diverted through the bonnet Carre Spillway (泄洪道 ). This is an emergency channel, controlled by floo
20、d gates, to Lake Pontchartrain, which empties into the Gulf of Mexico. Jetties and Cutoffs Jetties (防波堤 ) are piers or embankments designed to narrow the channel, and thus increase the scouring action of the current. They are particularly valuable at the mouth of the fiver to carry silt-laden waters
21、 out to sea. Cutoffs shorten and straighten the rivers channel. They speed up the rivers flow and thus lower flood stages upstream. On the Mississippi, cutoffs have reduced the river distance from Memphis, Tenn., to Vicksburg, Miss., by 170 miles and lowered the flood water high stage more than 12 f
22、eet at Arkansas City, Ark., and 6 feet at Vicksburg. Other channel improvements, such as widening and deepening, clearing out vegetation, and paving the banks, also increase the capacity of a river to carry off flood waters. In addition, these projects improve navigation. Dams and Reservoirs Dams an
23、d the reservoirs behind them help control floods. By emptying a dam before a flood is expected, storage space is obtained in which the flood waters can be impounded (贮存 ) for gradual release later. Even if the reservoir is nearly full, it acts like a safety valve. An amount of water, which would add
24、 ten feet to the height of a river 100 feet wide, would add only one foot to a reservoir or lake 1,000 feet wide. Moreover, evaporation from the broad surface of a reservoir or lake is far greater than evaporation from the narrow surface of a river. Thus less water flows on to swell floods downstrea
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- 外语类 试卷 大学 英语四 模拟 776 答案 解析 DOC
