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、 exstart state>exchange state>loading state>full state
• B、 exstart state>full state>loading state>exchange state
• C、 Loading state>exchange state>full state>exstart state
• D、 exstart state>loading state>exchange state>full state