About the description of the Keepalive message of BGP, which of the following is incorrect?

About the description of the Keepalive message of BGP, which of the following is incorrect?
A . Keepalive packet contains only one BGP data header
B . By default, the keepalive interval is 180s
C . Keepalive messages are mainly used to confirm the operating status of peer routers and the availability of links
D . Keepalive is periodically sent between two BGP neighbors

Answer: B