[单项选择]What eventually happened to the rich, powerful country 2000 years ago A. Its people died of hunger. B. It fell to pieces. C. It became a giant empire. D. It built many ships with wood.
第22题: [多项选择]对于机房UPS的要求有() A. 输入电压(V):220V±10%;输入频率(Hz):50Hz±5% B. 输出电压(V):220V±3%~220V±5% C. 输出频率(Hz):50Hz~60Hz;谐波失真:小于5% D. 输出波形:正弦波;工作方式:在线式;动态反应时间:小于2ms 参考答案:A, B, C, D