What is the primary function of NetFlow?

What is the primary function of NetFlow?

A.
NetFlow requires changes to the packet and provides statistics based on these packet flows.

B.
NetFlow identifies packet flows for both ingress and egress IP packets and provides statistics
based on these packet flows.

C.
NetFlow does not use flows to provide statistics for accounting.

D.
NetFlow does not use flows to provide statistics for network monitoring.