In a vPC (Virtual Port-Channel) environment, multicast traffic is expected to be replicated to the ports that have joined the multicast group and also across the peer link. This ensures that in case of a failure scenario, orphan ports, which are ports not part of the vPC and only connected to one of the vPC peer switches, still receive the multicast stream. Option C correctly describes this behavior, where the multicast traffic is replicated to the ports that joined a given multicast group and the peer link, and the multicast traffic stream flows over the peer link to ensure that orphan ports receive the multicast stream in failure scenarios12.
References: = For a more in-depth understanding of multicast traffic flow in a vPC environment, you can refer to Cisco's official documentation on multicast forwarding in vPC based on the location of the source1, as well as community discussions and technical articles available on the Cisco Community website