未知题型 防护中使用的移动停车信号?昼间为?（）夜间为（）。

单项选择题 WSN中常采用的时间同步协议是（）。

单项选择题 Last year China’s saving rate was 54 percent of GDP, according to China Daily. The U.S. rate, including households and corporations, was a mere 12 percent of GDP. What kind of statistics are used in the statement. A、Single statisticsB、Multiple statisticsC、Various statisticsD、none of the above