What would the first line in this debug serial interface output indicate?

A.
The mineseen HDLC sequence has missed more than three keepalives

B.
Keepalives are being received from the other end of a point-to-point link and this end is not sending them.

C.
The yourseen HDLC sequence number is out of order.

D.
The HDLC myseq has missed more than three keepalive messages, the WAN link keepalive activity will not occur, and you should expect to see a Layer 2 issue.