Where is BFD configured?

A network engineer is configuring IS-IS in Cisco IOS XR. Where is BFD configured?

A.
RP/0/RSP0/CPU0:router(config-isis-if)#

B.
RP/0/RSP0/CPU0:router(config)#

C.
RP/0/RSP0/CPU0:router(config-bfd)#

D.
RP/0/RSP0/CPU0:router(config-isis-if-af)#