I believe that the multiple questions attached to this question is
a) Hello
b) Link groups
c) Path groups
d) Heartbeats
The Answer is B and C
The physical interfaces that are supposed to be monitored are connected into a link group and a firewall failure can be triggered when one or all physical interfaces in the group failPath Monitoring helps monitor the full path to mission critical IP addresses. By default, any one of the IP addresses becoming unreachable will end up causing the firewall to change the HA to tentative state