What is the BGP synchronization rule?

What is the BGP synchronization rule?

A.
Routing information received through an IBGP session is not forwarded to another IBGP neighbor, only to EBGP neighbors.

B.
Routing information received through an EBGP session is not forwarded to another EBGP neighbor, only to IBGP neighbors.

C.
BGP neighbor peerings are established and sychronized using the TCP 3-way handshake.

D.
BGP shall not advertise a route until that route has been learned via an IGP also.