[外语类试卷]大学英语六级模拟试卷637及答案与解析.doc
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1、大学英语六级模拟试卷 637及答案与解析 一、 Part I Writing (30 minutes) 1 1. 现代生活充满压力 2. 压力的种种迹象 3. 如何减轻压力 How to Reduce Stress and Tension 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 att
2、ached to the passage. For questions 1-4, mark: Y (for YES) if the statement 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 Part Reading Comprehension
3、(Skimming and Scanning) Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1. For questions 1-7, choose the best answer from the four choices marked A), B), C) and D). For questions 8-10, complete the sentences with the informat
4、ion given in the passage. Satellite Today, you see compact satellite dishes perched on rooftops all over the United States. Drive through rural areas beyond the reach of the cable companies and youll find dishes on just about every house. The major satellite television companies are bringing in more
5、 customers every day with the lure of movies, sporting events and news from around the world. The Broadcast TV Problem Conceptually, satellite television is, a lot like broadcast television. Its a wireless system for delivering television programming directly to a viewers house. Both broadcast telev
6、ision and satellite stations transmit programming via a radio signal. Broadcast stations use a powerful antenna to transmit radio waves to the surrounding area. Viewers can pick up the signal with a much smaller antenna. The main limitation of broadcast television is range. The radio signals used to
7、 broadcast television shoot out from the broadcast antenna in a straight line. In order to receive these signals, you have to be in the direct “line of sight“ of the antenna. One problem is that the Earth is curved, so it eventually breaks the signals line of site. The other problem with broadcast t
8、elevision is that the signal is often distorted even in the viewing area. To get a perfectly clear signal like you find on cable, you have to be pretty close to the broadcast antenna without too many obstacles in the way. The Satellite TV Solution Satellite television solves the problems of range an
9、d distortion by transmitting broadcast signals from satellites orbiting the Earth. Since satellites are high in the sky, there are a lot more customers in the line of site. Satellite television systems transmit and receive radio signals using specialized antennas called satellite dishes. The televis
10、ion satellites are all in geosynchronous orbit, meaning that they stay in one place in the sky relative to the Earth. Each satellite is launched into space at about 7,000 mph (11,000kph), reaching approximately 22,200 miles (35,700km) above the Earth. At this speed and altitude, the satellite will r
11、evolve around the planet once every 24 hoursthe same period of time it takes the Earth to make one full rotation. In other words, the satellite keeps pace with our moving planet exactly. This way, you only have to direct the dish at the satellite once, and from then on it picks up the signal without
12、 adjustment, at least when everything works right. The Overall System Early satellite TV viewers were explorers of sorts. They used their expensive dishes to discover unique programming that wasnt necessarily intended for mass audiences. The dish and receiving equipment gave viewers the tools to pic
13、k up foreign stations, live feeding between different broadcast stations, NASA activities and a lot of other stuff transmitted using satellites. Some satellite owners still seek out this sort of programming on their own, but today, most satellite TV customers get their programming through a direct b
14、roadcast satellite (DBS) provider, such as Direct TV or the Dish Network. The provider selects programs and broadcasts them to subscribers as a set package. Basically, the providers goal is to bring dozens or even hundreds of channels to your television in a form that approximates the competition, c
15、able TV. Unlike earlier programming, the providers broadcast is completely digital, which means it has much better picture and sound quality. Early satellite television was broadcast in C-band radio radio in the 3.4-gigabertz (GHz) to 7-GHz frequency range. Digital broadcast satellite transmits prog
16、ramming in the Ku frequency range (12 GHz to 14 GHz ). The Programming Satellite TV providers get programming from two major sources: national turnaround channels (such as HBO, ESPN and CNN) and various local channels (NBC, CBS, ABC, PBS and Fox affiliates in a particular area). Most of the turnarou
17、nd channels also provide programming for cable television, and the local channels typically broadcast their programming over the airwaves. Turnaround channels usually have a distribution centre that beams their programming to a geostationary satellite. The broadcast centre uses large satellite dishe
18、s to pick up these analogs and digital signals from several sources. The broadcast centre converts all of this programming into a high-quality, uncompressed digital stream. At this point, the stream contains a vast quantity of dataabout 270 megabits per second (Mbps) for each channel. In order to tr
19、ansmit the signal from there, the broadcast centre has to compress it. Otherwise, it would be too big for the satellite to handle. Compression, Encryption and Transmission The two major providers in the United States use the MPEG-2 compressed video format the same format used to store movies on DVDs
20、. With MPEG-2 compression, the provider can reduce the 270-Mbps stream to about 5 or 10 Mbps (depending on the type of programming). This is the crucial step that has made DBS service a success. With digital compression, a typical satellite can transmit about 200 channels. Without digital compressio
21、n, it can transmit about 30 channels. At the broadcast centre, the high-quality digital stream of video goes through an MPEG-2 encoder, which converts the programming to MPEG-2 video of the correct size and format for the satellite receiver in your house. After the video is compressed, the provider
22、needs to encrypt it in order to keep people from accessing it for free. Encryption scrambles the digital data in such a way that it can only be decrypted (converted back into usable data) if the receiver has the correct decryption algorithm and security keys. Once the signal is compressed and encryp
23、ted, the broadcast centre beams it directly to one of its satellites. The satellite picks up the signal with an onboard dish, amplifies the signal and uses another dish to beam the signal back to the Earth, where viewers can pick it up. The Dish and the Receiver A satellite dish is just a special ki
24、nd of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam. The end component in t
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