Open Shortest Path First (OSPF) is a (66) routing algorithm that (67) work done on the OSI IS-IS intradomain routing protocol. This routing, as compared to distance-vector routing, requires (68) processing power. The (69) algorithm is used to calculate routes. OSPF routing table updates only take place when necessary, (70) at regular intervals.

A．distance-vector

B．link-state

C．flow-based

D．selective flooding