一台路由器接口信息显示如下: Serial0/0 current state: UP Line protocol current state: DOWN Physical layer is synchronous, Baudrate is 64000 bps Interface is DCE, Cable type is V.35, Clock mode is DCECLK 那么该接口上可能封装或运行了哪种协议? A. PPP B. HDLC C. Frame Relay D. RIP E. 以上答案都不正确