Default BGP keepalive timer in Junos is 30 seconds

The default keepalive time for BGP is 30 seconds, which means that BGP peers send keepalive messages to each other every 30 seconds to verify the liveness of the BGP session. If no keepalive message is received from a peer within the hold time, which is 90 seconds by default, the peer is considered to be unavailable and the BGP session is closed. The keepalive time and the hold time can be configured manually for each BGP peer or peer group, but they must match on both ends of the BGP session. The keepalive time should be one third of the hold time for optimal performance. Therefore, option C is correct and the other options are incorrect. References:  BGP keepalive messages and hold time - Juniper Networks

Option A is correct. Creating multiple areas in OSPF can help to reduce the convergence time . This is because changes in one area do not affect other areas, so fewer routers need to run the SPF algorithm in response to a change.

Option D is correct. Creating multiple areas in OSPF can help to reduce Link State Advertisement (LSA) flooding across the network. This is because LSAs are not flooded out of their area of origin.