CRH1A型动车组在正常运行过程中直流环节电压低于()V,IDU将显示直流环节欠压,并命令进行保护性关机。
A.1350
B.1450
C.1550
D.1650
参考答案:B
More than two hundred years ago the United States _______ from the British Empire and became an independent country.
A.broke down
B.broke out
C.broke away
D.broke off
防火墙是()在网络环境中的具体应用。
A.字符串匹配
B.入侵检测技术
C.访问控制技术
D.防病毒技术