The world’s biggest Internet search engine，Google，has proven once again to be king of the Web．Users can download“Google Wi-Fi”software and then enjoy free Wi-Fi service available in some US cities since last Tuesday．
Wi-Fi is short for“Wireless Fidelity”(无线上网)．It allows laptop computers and personal digital assistants to connect to the Internet at high speed by radio signal．
A person with a Wi-Fi enabled computer can connect to the Internet when near one of the network’s access points．The place covered by one or several access points is called a hotspot．Google has already set up two“hotspots”in the US city of San Francisco which provide a free Wi-Fi service．
The Wi—Fi technology even allows users to enjoy a free Internet phone service．
Some scientists argue that Wi-Fi may replace mobile phone networks．
Wi Fi is still limited to a few cities．where there are“hotspots”．But its capability (容量)of sending information has already done better than that of the mobile phone network，even that of 3G(Third Generation telecommunication technology)．Some scientists have started to call Wi-Fi 4G．
In addition to a high speed Internet connection，Wi-Fi has other advantages com pared to mobile phones．Wi-Fi is global．The same Wi-Fi system works in different countries around the world．Different from using cell phones，you don’t need to change computers to use Internet phones when you go to other places and most importantly，many Internet phones cost you nothing at all．
45．Wi-Fi is not available in cities without ．
A．a computer B．a radio C．a hotspot D．a cell phone
46．Which of the following is NOT the advantage of Wi-Fi?
A．The high speed Internet connection．
B．Many free Internet phones．
C．Using the same computers for Internet phones when you go to other places．
D．Used in all the US cities
47．Some scientists started to call Wi-Fi 4G，because ．
A．it is the product of the Google's 4th generation
B．it is more capable of sending information than the mobile phone network
C．it has been used by more than four generations
D．Wi-Fi will surely take the place of the mobile phone network
48．Which of the following is the best title?
A．Third Generation Telecommunication Technology
B．Free call Service
C．Google Launches Free Wi-Fi Service
D．Google， King of the Web
，得，
,A、B两行星的质量比为ab2 ：1,故A正确．
，则得到，甲、乙两行星表面的重力加速度之比为b2：a．故B正确．
,
则得，甲、乙两行星各自的卫星的最小周期之比为a：b，最大角速度之比为b：a．故C正确，D错误．