[外语类试卷]大学英语四级模拟试卷753(无答案).doc
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1、大学英语四级模拟试卷 753(无答案)一、Part I Writing (30 minutes)1 For this part, you are allowed 30 minutes to write a short essay entitled Limiting the Use of Disposable Plastic Bags. You should write at least 120 words following the outline given below in Chinese:1. 一次性塑料袋曾被广泛使用。 2. 使用一次性塑料袋带来的问题。 3. 限制使用一次性塑料袋的意
2、义。Limiting the Use of Disposable Plastic Bags _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
3、agrees with the information 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 Rocket RenaissanceThe Ear of Private Spaceflight Is About to StartBackgroundTwo years ago, people witnesse
4、d the first space travel by SpaceShip One. Three people were involved in this flight: Burt Rutan, who designed the craft, and Mike Melvill, who flew it-although they were ably assisted by Paul Allen, one of the founders of Microsoft, who paid for it. Certainly, people have long been known that manne
5、d spaceflight was possible. What they showed was that it is not just a game for governments. Private individuals can play, too.People involvedNow, lots of people want to join in, and most of them have just met up at the International Space Development Conference in Los Angeles, to engage in that mix
6、ture of camaraderie and competition that characterises the beginnings of a new technology. And, as might be expected, they have two of the necessary ingredients of success: ideas and money.First, the money. So far, more than $1 billion is known to have been committed to building private spaceships a
7、nd the infrastructure to support them. For example, Mr Rum s follow-up vehicle, SpaceShip Two, is expected to cost its backers, Virgin Galactic, $240m for a fleet of five. The spaceport in New Mexico from which these are intended to fly will account for another $225m, although New Mexicos government
8、 is planning to raise this money itself.These are not small sums, of course. On the other hand, Virgin Galactic has already banked $14m of deposits towards the $200,000 fare from people who want to travel on SpaceShip Two, even though it has yet to be built, let alone flown.All this suggests that sp
9、aceflight, if not exactly entering the age of the common man, is at least entering the age of the moderately prosperous enthusiast. For entrepreneurs, it is no longer necessary to have billions of dollars to get into space; millions will now do. And for those who merely wish to travel there, and hav
10、e enough money in their bank account, reality is favourable.Get startedAs with aircraft a century ago, a lot of designs are competing with each other, and there is no certainty about which will succeed. The initial goal is to build a “suborbital“ vehicle. This will not have to develop the tremendous
11、 speed needed to go into orbit around the Earth. instead, it will travel briefly into space, offering a short thrilling ride out of the atmosphere, a few minutes of weightlessness, and a spectacular view of the planet from about 100kin. Four important criteria are how you take off, what fuel you use
12、, what your craft is made of, and how you come back.Most peoples vision of a rocket launch is straight up from the ground. But, of the five vehicles most likely to be developed, two will actually be launched from the air. SpaceShip Two will be carded to high altitude by a purpose-built aircraft know
13、n as Eve before its rocket motor is ignited. And Explorer, a vehicle being designed by Space Adventures, will be launched from the top of a high-altitude Russian research plane called the M-55X, according to Eric Anderson, the firms president and chief executive.As Dennis Jenkins, a consultant engin
14、eer at NASA, Americas space agency, points out, this is similar to using a two-stage rocket to get into space, with the aircraft acting as the first stage. However, a plane offers several advantages over a throw-away booster rocket. First, it can be used again. Second, it uses oxygen from the air, r
15、ather than having to carry its own oxidant, which saves weight. Third, it is lifted by wings. That means the atmosphere is an advantage, rather than a hindrance. All this means that the spacecraft itself can be lighter and cheaper.Not everyone wants to run two vehicles, though. Jeff Greason, preside
16、nt of XCOR Aerospace, a firm based in Mojave, California, is developing a two-person, ground-launched suborbital rocketplane called Xerus. Launching from the ground, says Mr. Greason, is more difficult than air launching, but he reckons that in this case it has significantly lower operating costs.Fu
17、el choicesThe second important design choice is the type of fuel. Unlike a jet engine, a rocket carries its own oxidant (氧第剂). This is why it can operate in space. Sometimes that oxidant is oxygen itself, in liquid form. In that case the fuel, too, is usually liquid-either kerosene (煤油) or liquid hy
18、drogen (氢) and the two liquids are stored in separate tanks until they meet in the rockets combustion chamber. Alternatively, both fuel and oxidant are solid, and are loaded pre-mixed, like the propellant of a firework rocket.SpaceShip Two, though, follows the design of SpaceShip One and is powered
19、by a mixture of the two. The combustion chamber of a mixture is partly filled with solid fuel but no oxidant. However, the fuel is coated round the inside of the chamber, leaving a hole through the middle into which a liquid or gaseous oxidant can be pumped, and out of which the exhaust emerges. In
20、SpaceShip One, the fuel was rubber and the oxidant a liquefied gas called nitrous oxide (一氧化二氮).Proponents of mixture say they are safer than either pure solid or pure liquid rockets. George Whittinghill, Virgin Galactics chief technologist, says that they are safer than solid rockets because the fl
21、ow of oxidant can be controlled, and combustion halted, if there is a problem. Solid rockets, like the fireworks they resemble, cannot be stopped until they run out of fuel. On the other hand liquid-fuelled engines, though they can be shut down, are complex and temperamental. As Mr. Whittinghill obs
22、erves, “they have pumps, seals, valves and lines everywhere, and there is a lot that potentially could go wrong.“All this rather irrates those working on liquid propulsion. Richard Pournelle, head of investor relations at XCOR Aerospace, says the comparison is unfair. Liquid propulsion is routine in
23、 rocketry while hybrids are still rare. Numbers alone, therefore, mean that liquid-fuelled rockets blow up more often. That, Mr. Pournelle argues, does not prove that they are inherently unsafe. Chuck Lauer, vice- president of business development for Rocketplane, another firm going down the liquid-
24、fuelled route, agrees and argues that kerosene is widely used as aviation fuel and nobody complains that it is unsafe.2 It is only two years ago that people became aware of the fact that manned spaceflight was actually possible.(A)Y(B) N(C) NG3 Spaceflight is possible for individuals who want to fly
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