As a network administrator， can you tell me what the root guard feature provides in a bridgednetwork？（） ["It ensures that BPDUs sent by the root bridge are forwarded in a timely manner","It enforces the root bridge placement in the network","It ensures that all ports receiving BPDUs from the root bridge are in the forwarding state.","It ensures that the bridge is elected as root bridge in the network."]
冷战结束后，欧洲并没有获得一劳永逸的安全与稳定，中东欧地区冲突不断，成为流血的伤口。欧盟的软弱无能在波黑问题上暴露无遗，最终仍然需要美国的介入。这说明冷战结束后（）。 ["欧洲各国呈现衰落的迹象","美国成为世界上唯一超级大国","欧洲一体化程度亟待提高","美欧关系在全球化进程中加强"]
信用卡诈骗罪是指（） 。 ["伪造信用卡","变造信用卡","恶意透支","冒用他人的信用卡"]
原位生物修复
C220型号的OLT的mac默认老化时间是（） ["60s","120s","200s","300"]
载重量
