In the following essay, each blank has fou
题型：单项选择题
问题：
In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet.
Open Shortest Path First (OSPF) is a (1) routing algorithm that (2) work done on the OSI IS-IS intradomain routing protocol. This routing, as compared to distance-vector routing, requires (3) processing power. The (4) algorithm is used to calculate routes. OSPF routing table updates only take place when necessary, (5) at regular intervals.
1（）
A．distance-vector
B．link-state
C．flow-based
D．selective flooding