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【单选题】
Bluetooth When you use computers, entertainment systems or telephones, the various pieces and parts of the systems make up a community of electronic devices. These 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 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 networking 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 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 sending 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 telephone or television. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The Walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms. Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter(32-foot) radius you might think they'd interfere with one another, but it's 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 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 limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it's 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 Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second. Piconets(个人域网络) Let's say you have a typical modern living room with the typical modern Stuff inside. There's an entertainment system with a stereo, a DVD player, a satellite TV receiver and a television there's 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 has 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 the range, it responds, and a tiny network is formed. Now, even if one of these device
A.
Y
B.
N
C.
NG
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【单选题】包过滤路由器能够阻断的攻击是
A.
Teardrop
B.
SQL注入
C.
跨站脚本
D.
Cookie篡改
【多选题】(一)甲公司是专营进料加工的外商投资企业,该公司设在武汉.海关经营企业分类为B类。2007年6月该投资企业委托南京某进出口公司与韩国某企业签订一批原材料的进口合同,合同金额为800万美元,该批货物属于允许加工类商品。合同中已规定,40%进口料件加工成品内销,60%加工成品销往韩国,料件在7月底在上海入境。10月份该企业与韩国企业签订了加工成品出口合同,货物在杭州湾装船出境,出口日期为11月底。 根...
A.
发货人凭加盖“放行章”的装货单就可装货出境
B.
出口收汇核销单应在货物备好后就应向当地外管局领取
C.
合同核销必须在12月底前进行
D.
出口时无须提交加工贸易登记手册
【单选题】包过滤路由器能够阻断的攻击是
A.
Teardrop
B.
跨站脚本
C.
Cookie篡改
D.
SQL注入
【简答题】包过滤路由器能够阻断的攻击是 A)Teardrop B)跨站脚本 C)Cookie篡改 D)SQL注入
【简答题】我某公司与外商按CIF条件签订一笔大宗商品出口合同.合同规定装运期为8月份,但未规定具体开证日期。外商拖延开证,我方见装运期快到,从7月底开始,连续多次电催外商开证。8月5日。收到开证行简电通知,我方困怕耽误装运期,即按简电办理装运。8月28日,外方开来信用证正本。正本上对有关单据作了与合同不符的规定。我方审证时未予注意。交银行议付时,银行也未发现,开证行即以单证不符为由,拒付货款。你认为。我方应...
【多选题】甲公司是专营进料加工的外商投资企业,该公司设在武汉.海关经营企业分类为B类。2007年6月该投资企业委托南京某进出口公司与韩国某企业签订一批原材料的进口合同,合同金额为800万美元,该批货物属于允许加工类商品。合同中已规定,40%进口料件加工成品内销,60%加工成品销往韩国,料件在7月底在上海入境。10月份该企业与韩国企业签订了加工成品出口合同,货物在杭州湾装船出境,出口日期为11月底。 根据以上...
A.
发货人凭加盖“放行章”的装货单就可装货出境
B.
出口收汇核销单应在货物备好后就应向当地外管局领取
C.
合同核销必须在12月底前进行
D.
出口时无须提交加工贸易登记手册
【单选题】运动控制系统中广泛应用的动力源是()
A.
电气运动控制
B.
气液运动控制
C.
热机 运动控制
D.
混合运动控制
【判断题】拙政园因水成景,采用了“高方欲就亭台,低凹可开池沼”的方法。
A.
正确
B.
错误
【单选题】下面关于染色体数目变异的说法中,不正确的是
A.
同源三倍体一般都是高度不育的,但并非完全不能产生种子。
B.
同源四倍体不会产生部分不育。
C.
单倍体可以是三倍体。
D.
单倍体可能是一倍体,也可能不是一倍体。
【单选题】以下对加点字的解释错误的一项是()。
A.
百川灌河 河:指黄河
B.
至于北海 至于:到了
C.
期山东为三处 山东:山东省
D.
吾长见笑于大方之家 大方之家:明白大道理的人
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