闪光对焊焊接钢轨时，闪光的形成实质是（）不断形成和爆破过程，并在此过程中析出大量的热。
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什么设备可以对网络进行分段（）。
A. hub
B. 中继器
C. 交换机
D. 网桥
E. 路由器
F. 介质转换器
应用层可以提供基本的安全服务，只能单独提供，不能联合提供。
A. 正确
B. 错误
When learning a new route, if a LSA received is not found in the topological database, what will an internal OSPF router do?（）
A. The sequence numbers are checked, and if the LSA is val id it is entered into the topology database.
B. The LSA is placed in the topological database and an acknowledgement is sent to the transmitting router.
C. The LSA is dropped and a message is sent to the transmitting router.
D. The LSA is flooded imme diately out of all the OSPF interfaces, except the interface from which the LSA was received.
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