当路由器在经历了OSPF交换协议,它以什么顺序通过每个状态呢?()
A、A. exstart state>exchange state>loading state>full state
B、B. exstart state>full state>loading state>exchange state
C、C. Loading state>exchange state>full state>exstart state
D、D. exstart state>loading state>exchange state>full state