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When visitors to the Palace Museum feel a need to sit down for a cup of tea or find a bathroom without a long line, they soon will be able to turn to their smart phones for the information they need.This modern day solution comes thanks to an agreement signed on Friday by the museum and Huawei Co., the telecommunication giant, to build a “smart network” using 5G technology. Under the agreement, 5G Wi-Fi signals will cover the Palace Museum, China's royal palace from 1420 to 1911, and the branch museum of the institution under construction in northwestern Beijing.“It’s essential to alwa已知角的顶点与原点重合，始边与轴正半轴重合，终边在直线上，则的值为（ ）A． B． C． D．