Which action ensures prioritization of voice over data traffic?

Separate VLANs and subnets with QoS classification help segment traffic but do not by themselves guarantee prioritization without marking - classification alone does not enforce scheduling or queuing.

Placing voice and data on the same subnet without QoS classification provides no mechanism to differentiate or prioritize voice traffic over competing data flows.

CoS (Class of Service) is a Layer 2 QoS mechanism defined in IEEE 802.1p that marks traffic in the Ethernet frame header, while DSCP (Differentiated Services Code Point) is a Layer 3 mechanism that marks the IP packet header. Applying both ensures consistent QoS treatment across switched (Layer 2) and routed (Layer 3) segments of the network, giving voice traffic the low-latency, low-jitter forwarding it requires.

This option reverses the layer associations - DSCP belongs to Layer 3 (IP header) and CoS belongs to Layer 2 (Ethernet frame); swapping them describes an incorrect and non-functional configuration.