简述同生结核、成岩结核和后生结核的基本特征。
Which three Layer 2 access designs have all of their uplinks in an active state?（） [" Flex Links"," loop-free U"," looped square"," looped triangle"," loop-free inverted U"]
商品体
以下哪些项是工程建设增值主要表现为（） ["确保工程建设的安全","提高工程质量","有利于投资（成本）控制","有利于进度的控","确保工程使用安全"]
哪种设备可将本地 LAN 连接到地理上隔离的网络（） ["交换机","集线器","路由器","网桥"]
外模
