【名词&注释】
多媒体(multimedia)、功率因数校正(power factor correction)、开关电源(switching power supply)、有源功率因数(active power factor)、公用电话(public telephone)
[单选题]有源功率因数校正电路的主要优点包括（ ）。
A. 开关电源体积大
B. 功率因数较高
C. 低频电感大
D. 滤波器
查看答案&解析
举一反三：
[多选题]公用电话(public telephone)的种类包括（）。
A. 普通公用电话(public telephone)
B. 信息公用电话(public telephone)
C. 多媒体公用电话(public telephone)
D. IP公用电话(public telephone)
[多选题]4G is one of those terms that keep coming back through marketing brochures for what the latest technologies happen to be in the cellphone market. Every carrier claims to have true 4G, and has been claiming that for years, regardless of what they actually use. The reason was simple because the real 4G specification, expected to be drafted by the International Telecommunication Union, was no where to be found. In fact, the ITU took way longer than being expected to come up with a decision, likely because of massive lobbying campaigns. After all, which company wants to have to redesign its entire network just to be able to keep saying they are 4G? Now however, they ITU has decided itself.What does this mean for carriers and users? First，let’s see what 4G really is. As expected, LTE is central to the ITU strategy,but more precisely,the organization went with LTE-Advanced,which is a stricter version of traditional LTE. To qualify as 4G，a network has to provide 100Mbps connections over wireless,and 1 Gbps over wired. The whole network has to be fully IPv6 compliant. Frequencies have to be variable over 40MHz to avoid interference. Finally, global roaming has to be seamless, along with transitions between wirless and wired connections. This is a real step forward, and a good decision, which ensures that real 4G services will meet a good level of services. Technically, LTE-Advanced is just one of two new standard that are now under the umbrella called IMT-Advanced. The other one is WiMAX 2 which is a further refinement of the WimMAX protocol. Based on the paragraph above，to qualify as 4G, a network has to satisfy （） criteria. The transitions between wireless and wired connections have to be （）. LTE-Advanced is a standard belonging to （）.
A. two
B. three
C. four
D. five A．limited
E. possible
F. seamless
G. deployed A．WiMAX
H. WiMAX 2
I. IPv6
J. IMT-Advanced
[单选题]下列3G业务中，属于多媒体业务的是（ ）。[1分]
A. 紧急呼叫
B. 可视通话
C. 多方会话
D. 电路型传真
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