【单选题】
Which statement is correct regarding NBAR and NetFlow?()
A、NetFlow uses five key fields for the flow
B、NBAR examines data in Layers 3 and 4
C、NetFlow examines data in Layers 3 and 4
D、NBAR examines data in Layers 2 through 4
E、NetFlow examines data in Layers 2 through 4