On Cisco routers, how is hierarchical QoS implemented?

A.
Within the parent policy, reference another child policy using the policy-map command.

B.
Within the child policy, reference another parent policy using the policy-map command.

C.
Use the policy-map command within a service-policy to implement nested policy-maps.

D.
Within the parent policy-map, reference another child policy-map using the service-policy
command.