[外语类试卷]大学英语六级模拟试卷37及答案与解析.doc
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1、大学英语六级模拟试卷 37及答案与解析 一、 Part I Writing (30 minutes) 1 For this part, you are allowed 30 minutes to write a poster inviting freshmen to join a student association. You should write at least 150 words following the outline given below in Chinese: 1. 协会正在招募新成员 2. 协会的历史、宗旨和开展的活动 3. 如何加入,联系方式 二、 Part II R
2、eading 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 1-4, mark: Y (for YES) if the statement agrees with the information given in the passage; N (for
3、 NO) if the statement contradicts the information given in the passage; NG (for NOT GIVEN) if the information is not given in the passage. 2 Bluetooth When you use computers, entertainment systems or telephones, the various pieces and parts of the systems make up a community of electronic devices. T
4、hese devices communicate with each other using a variety of wires, cables, radio signals and infrared light(红外线 ) beams, and an even greater variety of connectors and plugs. The art of connecting things is becoming more and more complex every day. And Bluetooth has now become a new popular method of
5、 connecting devices that can streamline the process. A Bluetooth connection is wireless and automatic, and it takes small-area networking to the next level by removing the need for user intervention and keeping transmission power extremely low to save battery power. Bluetooth Operation Bluetooth net
6、working transmits data via 10w-power radio waves. It communicates on a frequency of 2.45 gigahertz(千兆赫 )(actually between 2.402 GHz and 2.480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices(ISM). A number
7、of devices that you may already use fake advantage of this same radio-frequency band. Baby monitors(微型监视器 ), garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band. One of the ways Bluetooth devices avoid interfering with other systems is by send
8、ing out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters(32 feet), cutting the chances of interference between your computer system and your portable telephon
9、e or television. Even with the low power, Bluetooth doesnt require line of sight between communicating devices. The Walls in your house wont stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms. Bluetooth can connect up to eight devices simultaneousl
10、y. With all of those devices in the same 10-meter(32-foot) radius; you might think theyd interfere with one another, but its unlikely. Bluetooth uses a technique called spread-spectrum.(扩展频谱 ) frequency that makes it rare for more than one device to be transmitting on the same frequency at the same
11、time. In this technique, a device will use. 79 individual, randomly chosen frequencies within a designated range, changing from one-to another on a regular basis. In the case of Bluetooth. the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a
12、limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, its unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetoo
13、th devices, since any interference on a particular frequency will last only a tiny fraction of a second. Piconets(个人域网络 ) Lets say you have a typical modern living room with the typical modern Stuff inside. Theres an entertainment system with a stereo, a DVD player, a satellite TV receiver and a tel
14、evision; theres also a cordless telephone and a-personal computer. Each of these systems uses Bluetooth, and each forms its own piconet to talk between the main unit and peripheral(外围设备 ). The cordless telephone has one Bluetooth transmitter in the base and another in the handset. The manufacturer h
15、as programmed each unit with an address that falls into a range of addresses it has established for a particular type of device. When the base is first turned on, it sends radio signals asking for a response from any units with an address in a particular range. Since the handset has an address in th
16、e range, it responds, and a tiny network is formed. Now, even if one of these devices should receive a signal from another system, it will ignore it since its not from within the network. The computer and entertainment system go through similar routines, establishing networks among addresses in rang
17、es established by manufacturers. Once the networks are established, the systems begin talking among themselves. Each piconet hops randomly through the available frequencies, so all of the pieonets are completely separated from one another. Now the living room has three separate networks established,
18、 each one made up of devices that know the address of transmitters it should listen to and the address of receivers it should talk to. Since each network is changing the frequency of its operation thousands of times a second, its unlikely that any two networks will be on the same frequency at the sa
19、me time. If it turns out that they are, then the resulting confusion will only cover a tiny fraction of a second, and software designed to correct for such errors weeds out the confusing information and gets on with the networks business. Bluetooth Security In any wireless networking setup, security
20、 is a concern. Devices can easily grab radio waves out of the air, so people who send sensitive information over a wireless connection need to take precautions to make sure those signals arent intercepted. Bluetooth technology is no different its wireless and therefore susceptible to spying and remo
21、te access, just like WiFi is susceptible if the network isnt secure. With Bluetooth, though, the automatic nature of the connection, which is a huge benefit in terms of time and effort, is also a benefit to people looking to send you data without your permission. Bluetooth offers several security mo
22、des, and device manufacturers determine which mode to include in a Bluetooth-enabled gadget(配件 ). In almost all cases, Bluetooth users can establish “trusted devices“ that can exchange data without asking permission. When any other device tries to establish a connection to the users gadget, the user
23、 has to decide to allow it. Service-level security and device-level security work together to protect Bluetooth devices from unauthorized data transmission. Security methods include authorization and identification procedures that limit the use of Bluetooth services to the registered user and requir
24、e that users make a conscious decision to open a file or accept a, data transfer. As long as these measures are enabled on the users phone or other device, unauthorized access is unlikely. A user can also simply switch his Bluetooth mode to “non-discoverable“ and avoid connecting with other Bluetoot
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