What is the likely cause?

It is noted in flow source view that some devices are showing “never received” in the last received flow column. It is verified that the flows are not being blocked by a firewall.

What is the likely cause?
A . flows are IPv6 and not supported by the network monitoring features
B . interface is no longer monitored by the network monitoring features
C . node is no longer monitored by the monitoring features
D . a primary field of data is missing and being dropped

Answer: D