题目内容：
●The metric assigned to each network depends on the type of protocol.Some simpleprotocol, like RIP, treats each network as equals.The（71）of passing through each network is the same;it is one（72） count.So if a packet passes through 10 network to reach the destination, the total cost is 10 hop counts.Other protocols, such as OSPF, allow the administrator to assign a cost for passing through a network based on the type of service require
D．A （73）through a network can have different costs（metrics）.For example, if maximum（74）is the desired type of service, a satellite link has a lower metric than a fiber-optic line.On the other hand, if minimum（75）is the desired type of service, a fiber-optic line has a lower metric than a satellite line.OSPF allow each router to have several routing table based on the required type of service.
（71）A．number
B．connection
C．diagram
D．cost
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